My advice is to stay away from the after-market TH clasps. They are OK, but are not anywhere near as good or accurately made as the genuine clasps. I will happily shell out AUD150 for a genuine clasp despite that being much more expensive than a clone.

For straps, the world is your oyster. There are plenty of alternatives for the more common straps, including variations on a theme, but if you are looking for straps for some the special/limited edition models you will need to pony up for the genuine article.