Try getting your hands on some Lidocain (not sure of the spelling).
I wouldn't use lidocaine. Its a local anesthetic only that has to either be injected or rubbed on the skin (if its in a transdermal form). You might mess up the ink of a tattoo doing either of those.
Also Lidocaine has a PH of about 2.5. It burns like a guy when injected until the numbing takes effect. Thats easy enough to counter act by buffering with Bicarb. If you've ever had stitches, thats the "numbing needle" that hurt like hell. For some reason it seems like human medicine doesn't believe in buffering lidocaine.
Again, I wouldn't use it. There are way better drugs--that and the fact its a tattoo. Maybe I'm a fatalist, but damn, if you want to wear the ink, you need to stand the pain.