Aherne746

So today I remembered I had locked up my onza trials bike about 3 years ago at work, and not touched it since. I bought it for £50. It needs pedals and new grips and it will ride (ordered) Its a onza spyrogyra so nothing mind blowing. How do I go about finding out what chain and sprockets I need. I was thinking about buying a separate set so that I could have a similar gearing to bmx for some street cruising. Any info about these bikes in general will be good. New to trials but not new to bikes. Thank you