Yep, you have a second rear adapter.

In a pinch, (if your shop has one) you can use a Hayes 16omm IS front adapter. Identical spacing in every way with the Avid adapters. Yes, it works. Done it many times. Since Hayes has been in the bike hydro business for longer than Avid, you may have better luck finding one of their adapters in stock somewhere, rather than ordering.

*caveat* this works with Hayes/Avid IS 160mm front and rear adapters. No idea on other sizes/brands.