You just have to find a print shop that will print on vellum or buy some vellum sheets and print it yourself on a home photo inkjet printer.
That said, many consumer-grade (home) printers don't have presets for vellum (meaning the printer won't apply ink to the surface of the vellum correctly) so you're probably better off finding a print shop that will print on vellum if you don't have a very nice printer that can be set for printing on vellum.
|Drano by Kukla|
from Colorful Abstract
|Contemplating by Eyefull Tour|
|Chanuka by RivkiLocker|
from Happy Holidays