The only over the counter elk tags that I know of here in Montana are the surplus of left over tags that are avaliable after the special drawings have been made, any left over tags after the drawing will be on a first come first serve basis, but in order to get these you gotta be lucky enough to get drawn for a license if your a non-resident. If you want to hunt here, a outfitter may be your best bet but you better hurry as time is running out.
I think some over the counter tags can be bought in Idaho, maybe you can shoot elknut an e-mail and he should be able to let you know about the availibity of tags there, I'm not really too sure myself, sometimes the best thing to do is go to the states homepage for the right imformation regarding licenses and tags and if you still can't find it, there is always a phone number avaliable. Good luck, Bobby