Normally I would get a frame made up to suit the picture, but that takes some time. So what I would do is try to get a surround to cut to size to put around the picture to match to a normal sized frame. Hope that makes sense?

This should be a fairly cheap way of going and will be quick.

Pop into a frame shop and they should be able to show you all the different coloured surrounds and then you can match one to your picture.