I agree that ECS has some great stuff (and some amazing deals right now) but not for clear corner markers/signals.
Check out eBay:
98-05 BEETLE FRONT+REAR SIDE MARKER BUMPER LIGHTS 03 04:eBay Motors (item 170427633588 end time Jan-08-10 13:16:44 PST)
I ordered these and installed them. Pics are here:
Wolfe and Sue's '98 White TDI, "Bugsy McLove"
These are not Crystal Clear lenses. They have a textured surface that diffuses the light (shows up the entire lens rather than just the bulb at night). On a white Beetle I think these look great, but on a darker color I'd probably go with Crystal Clear lenses.