Hi. The other guys took care of where to get it. You could also use rubber cement. I've tried both, and like neither. They both hold well enough, it's just removing the residue after that irks me. I have seen where some people screw their patterns/templates down. I find it much hander to nail those things down. Honest.
I make my own patterns/templates for whatever I want to rout out. I make as perfect a pattern as I can, with 1/2" plywood, then glue it to a rough cut piece, and when the glue is dry rout out a 1" thick pattern, using a pattern bit. I call mine patterns, not templates. Then I drill however many small holes completely thru it, as nail guides. The nail holes are hidden in the final product, so you can be random if you want. I prefer a nail hole pattern, so if I decide to put the nail holes in sight after, they will form a pattern of sorts, rather than just random holes. I use 1 1/4" thin nails. I usually do not drive them flat, but no biggie if you do. I try to leave about 1/8" out, the total number of nails, depending on a variety of things, type of wood, complexity of design, size, etc. So at times you need to keep a close eye on the nails as sometimes they start to drift out. I use a small, 6" long, flat bar nail puller, that is the best thing I have found to pull the nails, and it leaves them straight - unlike a hammer. If the nails are too far in to pull, no problem, you can easily work the end fo the puller between the work and pattern, and gently pry them apart a bit, sometimes far enough to just pull them apart with your hands, sometimes just enough to use the puller on the nails. I realize my way is not for everyone, but works for me. Most of my router work lately is with wooden figure banks.