Nonda and Countax seem to be the main ones for tractors, Husqvarna for the riders. I ended up with the latter and it’s been really good. B&S engine plus lots of generic bits so spares should be OK when I need them. I didn’t bother with the hydrostatic transmission and haven’t regretted it.
I’m sure as with lots of s/h garden machinery, there’s a lot of crap for sale so caveat emptor and all that.
<edit>. As above, Kubota is a good call but might be out of your price range. The local authorities use them and they do diesel/multi cyclinder etc but £££’s unless very long in the tooth. John Deere might also be worth a look but the low end stuff is just branded generic with a JD £ premium .