I had BTC before the BCH fork, but I forgot to claim the BCH and just spent all of the BTC on buying more BCH. Can I still claim the pre-fork BCH even though my wallet balance is now 0? It was stored in Electrum. Any advice is appreciated.
Despite your bitcoin wallet balance being 0, your cash balance on the same address should be non-zero. Check that with a cash blockchain explorer and then import your private keys into a cash wallet to access the coins.
https://blockchair.com/ should be able to show you both your BTC and BCH balances for the same address.
If your address still has the BCH, make sure when claiming that you don't send it to a BTC address by mistake!