I owe scifi a correction! He was originally asking about a slave cylinder and somehow this got off track to the master? The use of the term solenoid is a bit offputting, but perhaps correct in other areas of the planet?
Slave cylinders are a Maserati, Fiat Multipla Girling piece, (.750" bore). The Fiat X1/9 uses a mirror image casting that if installed on the GOose, needs spacers to keep from compressing the bore! I bought them new, to use the innards for rebuilding mine! There are at least three different rebuild kits, each with unique pistons and seals......but should be fine in our cars.
The master cylinder is also a Girling (.750" bore) that is still sold for short track racing cars! Roundy round dirt cars..... Gentleman in OH still sells them on eBay as such. No need for Chinese junk when you have good quality Girling bits new!!! Hopefully Girling did not go to the dark side for their manufacturing......!!!! Kits for these cylinders were found under a mid 80's Jeep truck listing. I still have 3-4 of these kits available...... They do not work in a Pantera......
Hope this clears the muddied water a bit!
These clutch pieces should be simple to find with very little digging! THANKFULLY!!! Although the availability of the rebuild kits is drying up quickly!