I have been busting my ass to find different size collets for my router and finally I ran across this site http://www.gpcollets.com/ .
I have a Ridgid model # 2930, a 2 1/4 hp router and they fit right in. All of the other collets I found require a chuck that ends up being too long even if it was cut down and not to mention the price.
I have included 2 pages from their catalog and on pg.15 they have a collet adapter for 1/8" bits that fits a 1/4" collet . On pg.20 you will see the highlighted collets.
Just to jet you know that I'm not tying to endorse anyone here, only trying to help.
I have a Ridgid Trimmer (1/4" collet), but I often use a rotozip adapter chuck to mount 1/8" shank bits. I'm sure a replacement collet would have less runout than the setscrew style adapter I'm using. I wonder if the AF-50 collet would fit my Ridgid Trimmer?
Take the thing out and compare the size to what's in the catalog. And if you can't find it , call the people. Think about it, if you design simple shop tools for a big company and normally you have to save them money as well, would you go out and design a special collet or would you find some already made. The minimum cost for setting up a simple production line is way more that what any company is willing to spend on a simple part that is not custom orientated. And I do not think that collets are so custom.
The part I have mentioned will not work with your trimmer.
I forgot to post this and just remembered. If you're using 1/8" bits, they have a collet adapter on pg.15 of their catalog that will fit your 1/4" collet. I saw some other adapters on sale, brass with a set screw, but I don't trust a holder that depends on a setscrew; just that will offset the bit.
The thing I did before I got the right collet was to edit my tool in the program and I would increase the diameter of the cutter to whatever the wobble created.