American Circuit Breaker was the last company to manufacture the FP Stab lock line (And yes they did all the correct UL testing), they closed the plant about 10 years ago but you can still find new surplus breakers on the market. Currently a company called UBI makes stab lok replacements, home depot carries them.
As mentioned Eaton makes about anything for replacement of old Westy breakers, they also have panel retrofits for the FP stab lok panels.
As mentioned, be careful about used or "reconditioned" small MCCB's, if you go that route ask for a complete test report. Dealers that are members of PEARL are certified to have correct test equipment and reconditioned procedures for MCCB's. Many of the so called dealers don't have the ability to test MCCB's and don't really stock much, they just go buy from the PEARL guys and resell. Astro Controls
www.astrocontrols.com is perhaps the largest PEARL certified dealer of molded case breakers in the country.
What specific breakers are you looking for? That would be helpful for offering advice.