All that Ive found is that "MAZDA 121 III (JASM, JBSM) 1996/03" valve stem seals will fit (8mm ID, 12mm Guide OD).

I'm not too sure that they're hard to find, my builder couldn't source any but that was with a rush on getting the head reconditioned.

Do you want the eBay link, bit of a waste buying all the way from J-pan or US but it may be your only option?

Nah I'd rather try and get something local first

I can tell you that A12GX Heads use the same valve stem seals as the later E15 Pulsar front wheel drive engines,Haven't tried them on a normal 1200 though.
These are used instead of the umbrella seals because of the space limitations with double valve springs.
With the single valve spring setup of a standard engine umbrella seals work OK,if it isn't broken don't fix it.
If the valve guides are worn you can either replace the guides which then need reaming to size or you can have them inserted with "K"line bronze inserts.
These are a bronze insert with an internal spiral to retain lubrication,they are actually swaged into place and are very reliable,just make sure the right people fit them and they will last longer than stock guides.
Having worked as both mechanic and a machinist in a race engine shop these are the go for most reconditioning,I would use new guides for any serious race engine just as a matter of principle though.

I went to my local engine head reconditoner/engine machinist and they had some in stock that fit - not sure off what car but I made a 12mm spigot with a 7.95mm parallel section and asked them to find a seal that fit.

I installed them and they work - no more oil burning at idle/revving then shutting throttle (high vac.) situations.

Carbs run a tad rich at idle and a tad lean at WOT (need a smaller pilot, drill main to No. 42 drill and raise needle 1 slot).

Just as I rolled into the driveway and went to turn the engine off the car just ran out of fuel...never trust a 1200 fuel gauge.