Don't be shy about asking random gym dudes for spots. For the most part, guys don't mind helping another lifter out, as long as you're serious about it. If you're one of those guys who bring the bar down to 3 inches above your chest, then push it back up, you'll annoy people. Otherwise, you should be fine.
And if you just aren't comfortable interrupting a guy to ask him to come over and spot you, try simply finding someone who is already benching, and ask if you can work in with him. If there's another guy benching alone, he might appreciate having a spotter for his lifts as well.
Oh, and I should probably throw in a more typical T-Nation answer....
Get some friends --> Have them spot you
Stop being a pussy, sack up, and push the damn weight yourself.