If you're using the Aspire tanks they use the 510 drip tip. And like bwh79 said most tanks, at least the majority of the ones I've come across, use these. I have both the nautilus and nautilus mini and swap out the drip tips between the two pretty frequently with no problem.
There are dozens of sites out there that offer drip tips in different colors, styles, shapes, sizes, etc. One of my favorite types is the
rotating head kind so I don't have to hold the device at a weird angle or tilt my head too much. (Quick note though, after using it for awhile the rotation becomes pretty loose. It stays attached no problem but it rotates very easily now as opposed to it being a stiff rotation at first. Understandable, just thought I'd mention it.)
Some sites you could check out:
MyVaporStore
Drip Tip Designz
Vivid Smoke
Vapor Beast
Good luck finding a new tip!