Sam Lam out of Canada also makes one, [email protected] This bushing may require a little fitting, as Sam makes them slightly oversized to improve hammer to bushing to pivot pin fit and improve the overall trigger feel.
Both Bam and Sam have been in contact with me over the years to ensure their products meet the original design. Sam Lam also makes a couple of very nice blank off plates for the Mark III's LCI slot. He and I have corresponded many times over the design of that part too.
I use the Mark II bushings from Clark Custom. They require just a bit of fitting to the pivot pin, but render a bit better trigger pull than a stock Mark II bushing, which can or at least could be gotten from Brownell's.