The sapfire tape guides I sourced from one-off NOS sale in Switzerland, those were used on some late model headblocks, and can still be found.
Sam, it is quite hard to find a good 15/30UPS machine, but if you can't, there is a relatively easy mod from 15 to 30 UPS (just google studer HS modification), for which you need some parts.
For location recording, I have chosen Nagra 4-S, a great machine for that purpose, running at .5/15 UPS. To be modifies along the lines of the Studers, space permitting (lots of tantal caps that must go, but a great design). My Nagra comes with a lot of ruby stones on the transport, the Swiss watch influence there, and the tape travel is remarkably stable, for the size of this jewel.
There are still quite many good Nagras fs in the US (mine came from a US studio). Very durable/reliable machines.
The A810 can also be used on location, it is "only" 35kg, and of a rather standard size, but the Nagra is way ahead in handling/size/weight, giving very similar sonic results on recording.
Best,
Tod