Our Home Depot stores have trial size samples to check with. But our Lowes seem to have a much larger selection in shallow drawers of odd sized metric bolts. Is there an exploded view diagram of the tool, sometimes they give dimensions, and occasionally I find parts sizes listed in the instruction book. I often find a pdf of these books online at the manufacturer's website, or you might email and ask if they have the part. Take a photo and attach it to your email so they know what you're asking about. I always mention being active on this Forum when I make such a request and that I will share the results with the rest of the gang. Thank them in advance for any help they can provide.
A couple of times I've gotten a free small part in reply, although I never expect it and always ask for the cost of a replacement.
The more I do, the less I accomplish.