how much you lookink to spend? You can get a used OE replacement fairly cheap; usually ~$150 maybe less. I saw a 749R clamp (adjustable for 36/30mm offset) in the classifeds for $650. Or, you can find a set of 27mm offset triples used for about that price; new they're around $800-1000
Do a search for all the intimate details, but in a nutshell less offset = more trail which gives more front end feel and stability at the expense of steering effort. This mainly comes into play when you change the steering geometry around to the 23.5 degree head setting.
If you're just looking to replace the top clamp, then you need to stick to the stock 36mm offset. There are aftermarket clamps from a number of sources: Speedymoto, Nichols and Motowheels come to mind.