You might try cbliss.com . They have many different free part models and I-parts. You might also try autodesk "point A" if you can find it on their website.
I agree : i found a chain on that site but i want to add some remarks :
1. If u want a longer chain u need to add the links urself in other words : each link is constrained => timeconsuming job if u want a long chain
2. It slows down ur pc the longer it gets.
3. U cant use the existing chain and copy it. The reason is that from the moment u change something in the direction of the links of one chain it makes the same change in the copies. Therefore this is too much a trial and error excercise.
Final solution i used : i took two links and used pattern to make a long straight chain. I was lucky this time i could use a straight one.
But...... are there other suggestions for designing a chain? I thought about designing a piece of chain and then sketch the route of the chain. Any suggestions?