Generally speaking the smallest most places carry are 1/8th size eyelets/grommets. However, I did find a source for 1/16 size ones I just don't have the URL with me at work. I know that the website is aimed at scrapbookers, not sewing, so maybe search some of those and see what you can come up with. But yea, I'd go 1/16 size ones for fashion dolls.
When I needed Grommets for my 25cm Dollfie EB Beauty Midi, I just wound thin craft wire around a toothpick a few times, then cut the wire and sewed the loop on. It's a pretty good substitute.