I just left employment with a LHS....let me shed some light on this for you...
1. sometimes the shop just doesn't have it, it just sold out etc etc...
2. at times the manufactuer will discontinue an item for a while...the distributor still has it, but with every shop in the nation ordering from a couple of distributors...it doesn't take long for it to become out of stock...
3. at times the distributor drops the ball, as well as the LHS, and doesn't order something...it's easier to say out of stock than ooopps...(this is rare)

These are some of the reasons not all....but there isn't some conspiracy to drive up prices or to get you to visit web sites......

Oh yea sometimes a distributors customer support will have a part, for those warrenity items that has not been released so that the distributor can ship out for orders to LHS...

Distributors will hold items ordered by LHS until the LHS order reaches a certain dollor amount.....all of these things slow the process of getting parts in your hands by your LHS...so the part is ordered not received.....it's out of stock