Weaver make a 2-piece set of bases.
Tasco used to make a 1-piece base for Weaver-style rings.
Leupold makes and Redfield used to make a 1-piece base for turn-in rings.
I prefer to use the Tasco BM-99 1-piece base with Warne Maxima rings on my 99s that have been factory d&t. Tasco BM-99s regularly show up on eBay for under $10.