Miyata 100M and 112M, from 1985 to 87 are triple butted CroMo main frames. 88 Miyata Valley Runner is triple-butted. By 1989 the Runner series all are STB (i.e. splined triple-butted) with varying qualities of fork.
It's interesting how often Mixte's are undervalued. Look at this listing:
https://www.kijiji.ca/v-cruiser-comm...ationFlag=true
That's a STB frame with a CRoMo fork for $70 CDN.