Yeah, Mactan Base is the only place to get it. (The Drome')
I thnk there is a good trade route available that well get you through all four systems, but I'm trying to figure it out, and I don't want Pirates involved

Diamonds from the system just outside of Frankfurt @ 300 each (Omega 5?), sell in Leeds (1275). SOMETHING from Leeds to New York, Detriot Munitions, Lightarms, to Battle Ship Matsumoto, then something from the Kusari area down to New Berlin (Only 3 jumps through Sigma 13)

Another good one is look at stuff for Cambridge, cos it has several high selling cargo needs.

Oh, and here's one. Can someone please tell me how much Diamonds sell in New Tokyo? Don't look it up, please go there in your game. I heard they were about 1600, but on mine they ain't...

If it wasn't for the inky blackness of the night you wouldn't appreciate the brilliance of the stars...

yes... how much would that make per trip?

This one takes a little patience, but pays well; First, bribe the Junkers & Zoners, & maybe Golden C., object being, to get as near neutral as you can with all factions, (see other spoilers). This is vital when mining. Get the Dromedary.
Go to Tau37, Malvinas cloud. Turn off "space dust" in menu. Shoot rocks. Takes about 20 minutues to fill a Drom. with niobium. Every rock has ore. Run that down to Leipzig sta., Dresden, sell for $440,000.00, pure profit. Drive over near the Frankfurt jump hole, and shoot rocks. Takes a long time to fill up with diamonds, (10% yield). Run that load to New Tokyo, and you've made near a million clear profit, minus the bribe money & cost of ship & equip. Pick out something nice for Falkland sta., in Tau37, and repeat the process. There are lots of good runs in this great game. This one works for me.

i find the best trade route just using the Dromedary freighter to transport cadramine to manhatten through the old magellan to new york jump gate. fast and you rarely get caught with the drugs.

I do sometimes an easy and leagal run wich starts at Planet New Berlin.
1. Take Diamonds to New Tokyo.
2. Take Niobium to The Ring.
That's my most used route, quick and easy, 4 Jumpgates (3 jumpholes in SP).
You can also strech the run from Bautzen Station in Dresden taking diamonds to New Tokyo. Then go to Planet Kyushu and take Niobium on the way back to Leipzig Station in Dresden.
A bit harder and longer, but a lot more profitable. Also You loot a lot from those Hessians In Dresden. All class 6/7/8
You need a good ship though.

And sometimes I take Engine Components from New Tokyo to FP4 (Not Mactan, bad rep with Hackers) or Cambridge and Gold from Dublin to Alster Shipyard in Hamburg. Then back to Dresden or New Berlin.

That's my route.

The Titan Flies Like A Cow

Before reinventing the wheel have a look at some of the older threads and experiment with the runs mentioned there:
Best Trade Route?! (Trade cycle!)
Getting a class 10 ship in 2 hours and 49 minutes
What is most profitable trade route and what and where is best shield no mod/hack??
Easiest and most profitable trade routes. Leave your opinions here!!

Once you have a Dromedary and a couple hundred thousand in the bank the only interesting measure for a trade route is the absolute profit per unit per minute (ppum) balanced by the risk according to your rep sheet, since you have enough capital to trade in any commodity.

However, if you are low on cash then other trades can be more lucrative - those where you buy at very low price and sell at a high relative profit. Liberty is a good starting point for such 'multiplier' trades, especially Luxury Consumer Goods, Light Arms and Boron. And if you are extremely low on cash then you may have to trade a low-value commodity like food or water for a while.

For example, if you respawn with a Dromedary and $4 in the bank then you do not have enough seed capital to use any of the usual trade routes. But if you are somewhere in Liberty then you can go to Battleship Yukon (California) or Battleship Rio Grande (Colorado), sell three nanos or batts and fill your hold with toxic waste. Total outlay: $550. Ship this to Dortmund Station in New Berlin and sell @ $200, for a profit of $53950. For the return run to New York pick up ship hull panels right there at Dortmund. This leaves a cash reserve of $10000 and the profit is only $10000 less than other trades that would drain your cash completely (and $110000 is nothing to sneeze at anyway).

Back in New York you have enough seed capital to go on the Manhattan-Ainu route and enter the Niobium/Diamonds run from there or do the Manhattan/Montezuma circuit if your rep permits, and you have an extra $100000 in the bank as insurance against accidents.