Hi Feeble,
there is no problem at all to run a "normal" BMX chain (1/8") on a driver or sprocket which is made for 3/32" (narrow) chains. The teeth are just 3 mm wide for 1/8" chains and 2 mm for 3/32" chains. So the chain would have some side-to-side play, but this should not be a problem. So you could just buy a 1/8" chain...
But: These are heavier and from my experience a high quality 3/32" chain does the job for flatland. What I did several times: Grind down the teeth of the sprocket to 2 mm width! With a belt sander it is just some time you need to spend. Of course the sprocket does not look so nice any more, but if you do it on the "backside" I think you can accept this. This would be the easiest way.