You should just check out a construction company around you and see where they get there slings from. You seem to be asking for an eye to eye nylon sling or twisted eye might be better for your purpose. Most crane companies and rigging companies can supply the good stuff, but your better off getting from the manufacturer..most slings are required to have the weight ratings and manufacturer on the strap its self if used commercially / industrially ....so you can see who made it if you go see one, and know what its capacities are in different lift or pulling configurations.
Here's a local manufacturer near me.
http://www.saturnind.com/slings.php
Custom stuff is available also.
But you probably have something closer and might not know where to start looking.
Anyway there's a manaufacturer who does this kind of thing....not my company...just info.
Most of the industrial stuff is pricey due to liability issues...you might be better off finding a surplus or implement store as Mudder67 replied.