Check almost any office supply store and/or hardware store glue department.
The stuff is used to stick posters on the wall without making holes. Borden makes a product which is orange and (IIRC) 3M makes a white product. Used both, both for sticking and for camo masking with no problems.
The kids who work at the local Staples office supply store are almost too helpful. Walk in and say you want some "Blu-Tac or similar, the stuff used to stick posters on the wall" and they will lead you to the aisle and show you their selection