Are there thinner grips available for the 228/229 frames? Got a short trigger, but some thinner grips would help my grip a bit as well.

Thanks!

...or, does anyone know of an outfit that offers a gip-slimming service much like Robar and their Glock grip slimming?

If you take the grip off the P-228/229, it does not get any more slimmer then the way it is now. Hogue rubber grip only enlarge the overall dimention of the grip (I have one so I know). If smaller grip is what's necessary for you, suggest go to like P-239 instead.

Robar's grip slimming service does not apply to metal frame handgun like SIG, glock can be done that way because of the polymer frame and striker design (the back of Glock grip is basically hollow out to form general fit for most shooter's hand, not so much the same case for HK USP as they need to use that space to house hammer spring)