I have a ceramic Cyrix 5x86-120GP 026-3.6V from 1995, got it from a coworker 11+ years ago when he purchased a P233MMX systemboard from me and was junking his old gear.
All the Cyrix 5x86 chips were hard to find since they came out very late in the 486 era and you needed decent PCI motherboards with the correct cache method and to enable functions to get the most speed from them.
I never heard of the 133 version, but if the were surface mount only I can see why since I only dealt with removable chips at the time these would have been new. Most people were using Pentiums at that point anyway.
http://web.archive.org/web/19970524022018/www.cyrix.com/process/prodinfo/legacy/5x-mblst.htm Shows boards that support the chip.
Dang...that compatibility list is really short!
I got plenty socket 3 PCI boards but only the SP3 is on that list, and that one blew up a couple weeks ago, don't know for sure if it'll work or not (posted topic on vogons about my SP3 board)