I probably should have mentioned this a while ago, but if you go into my house in Hobbiton and down the mineshaft in it you'll find a cave spider spawner. If anyone wants to use this to farm string/spider eyes feel free to. I blocked of all other caves/tunnels down there so it's impossible to miss. The front door is unreinforced, so feel free to wander in and get to work.

There also used to be a mineshaft going down from Simbarabbits house which had one near the bottom, but the entrance may be covered and the tunnels down there are a bit of a mess, so good luck trying to find it. I remember seeing at least one more spawner, but can't remember where. however I dont think any are close enough for a double-spawner-grinder