EDIT: Silly me, I can simply create a new wallet locally, transfer my coins there, and then use the old wallet to claim those forkcoins, right? Sorry to be such a pest, but I need to be 100% positive that I'm not missing something.
You could... but the issue is that you still need to download the forkcoin blockchain if you want to use the wallet.dat... (and in the case of BCH or BCHA or BCHN or whatever the hell it's called these days), that is quite a significant amount of data (not quite as big as Bitcoin Core, but it's still a couple of hundred gigs 
).If you create a "new_wallet.dat" in Bitcoin Core, then move all your BTC from your old wallet.dat to an address in "new_wallet.dat"... then you could simply use the dumpwallet or dumpprivkey on the old wallet.dat file to get the private keys you need.
You can then use any of the wallets that LoyceV listed above to import those keys and get the fork coins.
The important part is to move all your BTC to a completely new wallet.dat first... and then start messing about with claiming forkcoins.