At most local home improvement stores you should find the parts necessary. Although like Sean noted 1.5 inch to 3/4 is about a 4 times reduction in flow rate, not to mention hose bibs often start at 1/2 inch or smaller at the valve. If your going to try it once you get to 3/4 or so add a "T" and put two hose bibs on it, that way you can at least run out 2 3/4 inch hoses, about 1/2 the flow of a 1.5 inch.