Hmmm... this sounds like a joke to me, so here's my solution. If there is a pool to be decommisioned, you can try this recepie:
1. Take 1Kg divers lead, and with angle grinder and knife try getting the round shape
2. Take a water resistant duck tape, and try to make it look like a puck. If this doesnt work, then use silicon.
There's bound to be more recepies like this one out there...
Other than solutions like this, one needs a tool for lead, another tool for plastics, a machine to fill plastics, and if its a puck with discs - a machine to shape plastic disk or another tool to make plastic discs, plus a boaring machine,few screws and several general hand tools. Experiance in doing this process is... well... at least desirable, and damn cost efective!
A puck is under high mechanical stress & abrasion, and has to remain its shape for long periods of time. Becouse we play with professionally produced pucks, is the reason why pool bosses let us play UWH in their pools! In the late 70's there was a group of divers in Slovenia trying to play something like prehistoric-UWH in one of our pools, just to be forbidden to try it again, as they used home-made puck, that by the end of first game, ruined the tiles on the bottom. (Back than it was a concrete pool.... so they destroyed the bottom)
Conclusion.... If you had to ask how to do it, then my advice is: Dont do it!