How about auditioning a thin black/dark border (say 1/4" - 1/2" in width) and then audition that fabric you have bought from ebay and finish it off with another black/dark border? It may work quilt well as that fabric has the colours in your quilt though I agree that there needs to be some 'break up' of the colours (does this make sense?). You may find that wider dark borders work better? Best of luck choosing the fabrics for your border.