I got the strap from my local AD. The MSRP is 250 but if you have a good relationship with them you can work the price down. If you're hesitant to change the strap yourself the dealer will do it for you. It's not hard, but the rubber actually fits very tightly and has curved springbars, so it can be a little tricky.
I know the price seems like a lot to ask for a rubber strap, but 1.) it's a luxury product, so prepare to pay luxury prices for accessories (the Omega NATO straps are around 150 bucks!) and 2.) it really is an excellent strap. It's soft and supple. My favorite feature is this little nub on the inside of the sliding keeper that locks into the holes on the strap so it doesn't move while you're wearing the watch. It's Brilliant.