Is there any battery holder on the market that takes 10 AA but delivers 7.5V? The 5 AA holders don't seem to provide enough current for my purposes but every 10AA holder I've seen just delivers 15V.
You could modify the wiring of a 10AA series holder so that it becomes a pair of 5 AA holders in parallel
How much current do you actually need at 7.5V and what are you using it for ?
…or of course, there are other larger cells than AA
Paralleling consumer batteries is fraught with peril.
If you need higher current, use a different type of cell - good NiMH batteries should be able to provide more current than the usual alkaline, and high-current NiCds even more (although NiCds are generally disappointing in other respects.) You might need a 6AA holder to get 7.2V, though.
There are a range of high current capable NiMh battery packs sold for use in electric model RC cars etc.
I still have some packs of AA NiMh that I used for a small electric RC plane, they seemed quite happy putting out 8A or so ........
But not necessarily as efficient as AA. 
Some fake "C" cells actually contain an AA! (They are the same length, you know!)
I am old enough to recall "B" cells. 
Very true…
I too remember those old ‘Eveready’ zinc-carbon batteries wrapped in cardboard - for valve radios!
I was not really thinking about Cs (they were awful batteries), but there a lot of interesting primary and secondary cells out there.
Hi,
Instead of looking for 10 AA holder.
Look for
4 AA holder
1 AA holder
They are available, and construct your own pack.
Tom... 
If you have a 15V battery pack and want 7.5V you could use a buck converter.
For high current, you could use a 2S LiPo pack.
The OP is so far MIA, but what occurs to me is why 7.5 V?
I do trust/ hope it is not to power an Arduino (UNO, Nano, Mega, Leonardo etc.) from "Vin" or the "barrel jack" in the forlorn expectation that the battery is not providing sufficient current! 