Lots of 845G chipsets on ebay which work well with ISA sound cards. I own two of these boards and have tested personally with a GUS and several ISA Sound Blasters.
Amibay has a listing for this board (disclaimer: my listing):
http://www.amibay.com/showthread.php?t=38559
The key isn't to look at the chipset but rather the I/O bridge. The last bridge to support ISA devices before this feature was removed by Intel is the "ICH5".
However, ISA slots are STILL ok all the way up to the Intel 945 chipset if you want to support Windows 98se as the the minimum Windows OS. There are unofficial chipset drivers available for this board which work fine with a little bit of tweaking (also tested personally).
ISA bus mastering is only important for digital audio. No MIDI devices that I'm aware of use it. So, you can mix an ISA card for MIDI and a PCI card for sound effects. If I remember correctly regarding PCI card backwards compatibility for DOS, it's always the midi that has a problem since the cards are trying to emulate an entire MIDI synth which would never be accurate or have any variety. Digital sound effects are always more or less the same. It's the MIDI that has a wide range of possibility depending on your synth.
I have had a hunch that it should be possible to support a fully backwards compatible ISA slot on an i945 chipset with an I/O bridge newer than ICH5 as long as there is a DMA-compatible third-party PCI-ISA Bridge chip on the board as well. I actually have a i945+ICH7 board in the mail which should arrive today which has such a combination. So we shall see. 🤣