Sometimes see them on eBay....just have to keep your eyes open. Notice there's not any there now unless you don't care about reinstalling the air bag...in other words, not specifically Volvo steering wheel. Of course the dealer can order you one but they are EXPENSIVE to say the least. I can probably even find you a part number if you're really interested in such.
There are several options. These are all official Volvo part numbers:
9173437: Walnut, black
9173437(KN): Walnut, red
9192623: Oak, Oak leather
9192624: Dark Wood Walnut leather
9192625: Wood, black leather
9192626: Birch wood
I've listed them just as they appear (for P1 S/V 70's) in a parts manual, so I don't know exactly what these mean. You should confirm with your dealer if you want to order from them by going the expensive route.