Dwfisk, the Top Block should be very easy to come by. I am pretty sure all butchers get top sirloin sub-primals in. Just get them to cut a thick slice off of one. If you are looking for the old style, use a full, bone-on Prime Rib. They are delicious done this way. Due to their sudden popularity, tri-tip will be the hardest to find.
me: I don't drink anymore
Yelonutz: me either, but, then again, I don't drink any less