if its talking that you miss, but you all are still allowed to talk, then talk. Of course it has to be about work since everybody is keeping it all business now. For those work related issues where you previously didn't care to talk about (because that time was filled talking about more fun stuff), visit your colleagues and talk about them. That means give your opinions on how various issues affect the job, then give solutions, e.t.c
If there's a new printer at the office talk about how it prints so much slower than the previous printer. You have to balance this (negative, complaining, e.t.c) with suggestions and new ideas (...show coworkers new ideas, e.t.c). It's still all about work but it's talking. Try it a few times and you'll get the hang of it.