HP Natural Tracing Paper, 90 gsm, prints nice on the HP Z models. It has an inkjet coating. Whether that falls in the category of "vellum"and its substitutes is something I can not judge.
There is a HP Vellum , 100% rag, that I have no experience with.
Canson uses the Opalux name for its vellum quality, 100% rage based, 180 gsm, but no mention of an inkjet coating.
Schoellershammer, Océ, Canon, have vellum qualities.
met vriendelijke groeten, Ernst Dinkla
Dinkla Gallery Canvas Wrap Actions for Photoshop
http://www.pigment-print.com/dinklacanvaswraps/index.html