This is fairly easy and I'm sure was covered in the "this has everything" newbie sticky post but...

If you get SubZero's Freelancer Database (an absolutely essential list of all things in Freelancer, downloadable from this forum) you would find that the Sabre is a bw_elite2 which become a bwe2_package in the goods.ini file and the Anubis is an or_elite which becomes an oe_package in the goods.ini file.

Thus, when you go to market_ships.ini to change the ships those are the packages you look for (assuming you have bini or bini lite and have run it on the market_ships.ini file or have substituted the market_ships.ini file from the SDK files, also available for download from this forum, so it is no longer encrypted). To make them available to anyone from the beginning of the game you would look for marketgood = bwe2_package, 30, -1, 0, 0, 1, 1, 1 for instance and change it to: oe_package, 0, -1, 1, 1, 0, 1, 1 instead. That would make it available to you from the beginning no matter what your rank or freindliness or empathy to the faction your buying from. If you do that, substituting the oe_package for the bwe2_package you would make the Sabre unavailable for sale anywhere and have Anubis' instead. Of course this would not keep NPC's from using them if indeed they do (I haven't really looked lately to see) but no players would be able to buy one.