This might be what you are locking for:
Rytan has a set of mini picks that are amazingly small. Here is a video of these things side by side with Southord and Peterson picks. They are locksmith exclusive but I have seen them sold second hand if you are just a hobbyist. These are the smallest I have come across and they are not a brand that I really hear to much about.
Check out the video and see if this is what you are looking for, at the very least you can see what some of the other brands look like. The guy says that they are good for European locks, and those have very narrow key ways.
https://www.youtube.com/watch?v=hfU64zOMSesAt like 2:40 he actually starts talking about the Rytans.
Hope that helps.
(I edited this because I just noticed that the last guy to post mentioned them, but the link is still a great tool)