There are still some options around I think, this one for example: DIY Resin tank for SLA 3D Printer for Form1 form 1+ | eBay
I can’t speak to quality etc for that one specifically, but both them and Z-Vat should still be available (Shop Z-Vat Glass Resin Tank for Formlabs 3-D Printers)
The vat is a pretty simple thing though, so if you’re willing to put in some time I’m sure you could make one out of laser-cut acrylic and a PDMS pour.
There is also the Peopoly Moai vat, if that’s something you can find: Peopoly Moai FEP Vat in Form1/1+ without mechanical levelling
Good luck! I don’t regret a second of the work I put in to get mine functional, it is still a very dependable and accurate printer despite it’s age 