Feed a "solar" charge controller from AC->DC power supply?
That sounds like a good idea if you can't find a "proper charger" - which certainly do exist. 

Some of the solar chargers are very good, with equalisation cycles and more. 

I can't immediately think of any disadvantage of doing this. 12V solar chargers are designed to take Vin of at least 18V and probably 20V+. If you get one with "proper: MPPT it will probably allow you to get maximum charge out of a given voltage source. I say 'proper" MPPT as some of the new controllers use quasi MPPT where they load the source to a specified percentage of source Voc, based on typical PV panel load curves. This may well not be the true MPPT point for a semi random power source and worst case may cause loading issues - but probably not.

Large range of typical solar regulators - Australia

MPPT controller with discussion - USA, CA.

BP GCR series learning controllers - may be too smart in this role?

Lead acid charging tutorial bulk, absorption and float ...