Have you tried turning the truecolour map on with
/worldconfig colorAccurateWorldmap true
and looking for clay that way? It will be a slightly different shade than the grass. Here's a picture, for an example:
If you've explored for hours, you likely have enough of the map that you can look around, zoomed in, and should be able to find some clay that way. If you've already done that, I don't know what advice to give you, other than run around filling in as much of the map as you can. You could also find some other things to do - building is impeded due to the lack of metal tools, but you can start farming and build wooden structures, while you search for clay.
(You can also make new topics.)
Personally I find the difficulties (compared to Minecraft) make the game much more fun. Easy games are less satisfying... Keep playing, but if you continue to have this frustration, you can likely get a refund.