When you say 'unable to size' do you mean you can't get a good fit? If so, I completely understand your pain. I have 7 inch wrists and the bracelet was either too tight or too loose. It could really do with a few more macro adjust settings on the clasp. Fabulous watch despite this.
Regarding alternative straps, I tried mine on a brown Hirsch Liberty but it didn't look anywhere near as good as it does on the bracelet so mine went back on the bracelet and stayed on it until I sold it recently.
Word of caution, it may just be me being rubbish but I had a right ball ache trying to get the bracelet on and off. In fact, the bracelet didn't sit correct in the lug holes when I put it back on. A long standing independent watch maker/repairer (who also happens to be an accredited Rolex service centre) couldn't seat the spring bar correctly either and only Seiko UK managed to sort it out when I sent the watch in for a warranty repair.
If you are going to put youself through the trauma of a strap change, make sure you tape up the lugs to minimise the risk of damaging them and ffs take your time.