You can still buy new manufacture motherboards with ISA slots and modern processors. Intel still (or until recently) made ISA bridge chips for modern Southbridge chips. And it's something that a smallish FPGA could handle. There is a whole ecosystem of companies that recreate old-style motherboards for exactly this scenario.
My brother's company does IT stuff for the manufacturing sector. Very conservative. I've worked with a number of his customers to source exactly this sort of thing. Years ago they asked my thoughts on an Italian made cloth dying machine the size of a bus with a DOS PC controller and a minimally documented ISA controller. A mid 7-figure US$ setup; the company that built it is long gone. We found a shop that supplied new motherboards, modern (at the time...P3/P4 era I think) with ISA slots the vendor guaranteed it would be every bit as slow and weird as a PC/AT. Migrated everrything over, the company bought a stack of motherboard spares new, and I think they're still using them.
Now...you want a challenge? Migrating the proprietary, mostly undocumented software, all in Italian (we aren't native speakers...though my high school Latin occasionally helped) from an old ESDI disk to something, anything, else. That was much more interesting.