Hi I find this ----thetortoisetable.org.uk very useful it has a list of plants that are and aren't ok for them to eat, my greek is a bit fussy to, he loves dandelions the best and I just keep trying different foods and he's eventually becoming better with new things
Tortoise supply is where I got my little guy. And just bought that seed mix! Also got mazuri I know that's what they were feeding him. Tried zoo med grassland food but he wants nothing to do with it.