I'm using my no brand s3 armband. (was using an s3 before getting the nexus 4) Anyway, the headphone jack hole placement is slightly off, but you can still connect your earphones through it without much difficulty. The phone fits snugly enough in the armband too. Hence, if you can't wait till a n4 armband is available, just use the s3 one. It gets the job done.
Sent from my Nexus 4