My bogen tripod head did not come with a bubble level, but I believe I have seen them someplace that you can buy separately. I guess it doesn't have to be a bogen bubble, just a run-of-the-mill generic one, right? Any stores that might have them or ideas?

Any hardware type store, Home Depot.

I found a little stick-on bubble level at a local camera shop in a rack full of accessories. Only cost a few bucks and it works great. Unfortunately that was several years ago, and there is no manufacturer's name on the level...

I've searched the web repeatedly for a nice small one. (I bought a few of the hardware store variety, but either the circumference or height/thickness has always been larger than my equipment has room for). I'd like to get some about the size of a dime or an M&M.

It seems that the instrument manufacturers are the only ones who have access to them. I found one in UK who sold them only in large quantities, but they never responded to my email.

Perhaps you'd have better luck than me. Please share your findings.

I looked at B&H and found the level I've got:

http://www.bhphotovideo.com/bnh/controller/home?O=Search&A=details&Q=&sku=318714&is=REG&addedTroughType=search

Maybe a little larger than you want though, about 1 inch in diameter.

Google "spirit level" round

Ex. http://www.leveldevelopments.com/surface-mounted-circular-levels.htm

I purchased one from Home Depot, which I will be returning because it is about 1.5 inches in diameter. I am going to try the camera stores and see (Henry's etc), but I was also turned on "RV" stores because I guess they carry stuff like that for leveling out RV and fridges or something? I am going to check that this week.
I wish my Bogen Tripod had the level - I need the DIME sized solution for a bubble - even the 20mm from the catalog you mention is a little big. I thought I saw Button sized ones in other tripods like this :
http://www.hankinslawrenceimages.com/newsletter/articles/level.htm (on the bottom, on the left)

But I guess it is a matter of finding them.

Spare Manfrotto/Bogen tripod level bubbles for $6! (http://gallery.bcentral.com/GID2025592P4980947-Bubble-Level-for-Bogen-3033-3036-3046-3051-3068.aspx)

Cheers,
T

Thanks Toenis, that is a great link!