I have a 52mm ebay flat bottom tamper and my 58mm RB flat bottom tamper but no 53, not even the plastic junk. But I did have this 'thing' on the front of my other Compak doser that looked like it was smaller than a 58 but bigger than 52, sur enough it was a 57mm thing. It attached to the front of the doser for 'lift tamping'. I pulled out a cordless drill and with a file turned it down to 53.5. 1 to see if it fit the basket before ordering my RB C-flat and to get me by. It needed a handle though, and offly the 'legs' I bought for my Expobar I never used had a threaded hole and wouldn't ya know it screwed in. This wont polish but it will pack the basket. NSEW tamp backfired and I have to polish with my 52mm but hey it'll get me by for the week(s) or so that the RB will take to arrive.
Behold "Franken Tamper"