Menards should carry something like that. You can also probably find it at a Sears, Lowe's, a Linen's N Things or a Bed, Bath & Beyond...
Flowerbelle and Shelly started hopping up on the counters. We covered them with stuff for about a month. It was a pain in the butt, because we always had to move something to use them, but it worked (mostly).
How to stop him jumping onto that edge of counter and then into the sink? That I don't know. But sounds like a sink stopper would be a good idea.
Shelly still ocassionally jumps up onto the counters - but he always manages to jump down just as we're walking into the kitchen - and he KNOWS he wasn't supposed to have been up there because he BOLTS out of the kitchen after that, lol! Before, we'd say "NO" kind of loud and sternly, pick him (or Flowerbelle) up and set them on the floor. Of course, that only works when you're around to catch them. That's when we decided to cover the counters with so much stuff there wasn't anything to jump up on to.
Flowerbelle doesn't jump up there anymore. But Shelly likes to sneak a jump in every once in a while, even though he definitely got that he's not supposed to.