If you need this, I think the upside down cereal bowl is a better suggestion. Or the saucer that goes under a coffee cup.
More seriously, maybe it is just me, but when I cleaned a record, I left it on the record cleaner until the other disc was out of the way. Or I somehow managed to re-sleeve the disc on the platter prior to pulling out the next record. Somehow I don't think I ever got that mixed up and needed a transit puck.
Speaking of which a hockey puck would be just about the right size for this. Heavy enough not to slide around, a soft surface for the label area, and very easy to screw in something for the spindle if you want it to have a spindle.