How do you lace a zipp 808 that has a 20 spoke count when the only hubs that PT sells only go down to 24 count.
You could use a 24 hole hub and lace it 12 2 cross on the drive side and 8 radial on the non-drive side…of course PT won’t recommend any such thing and I think Zipp doesn’t recommend it either but it will work fine. 
PT are available in 20H. Maybe not at the particular retailer you are looking at but my '09 order forms have them (full disclosure, I’m a PT dealer). I doubt many places, even large online retailers, stock them.
Send it to Wheelbuilders and let them do it right.
Yup, you can get a PT in 20H. Just built mine up last week in an 808 rim. I would have a shop do it, or they can order one straight from Zipp that way. This will save you or them a lot of time and headache. Lacing that wheel is not fun if you want the bladed Sapim spokes.
Send it to Wheelbuilders and let them do it right.
+1