Shops of any decent size can order directly from Shimano and Shimano is giving more priority in ordering to local shops now actually. Some of the big online places may have some older stock still, but when they are out they will be ordering replacements from the same place the shops are. Shimano is also rationing. Our recent order for 35 cassettes was cut ~2/3 to 10 for now. We also are now buying bulk chain on 250 foot rolls and are cutting to length as needed with no waste (and no packaging to throw away). We never did that before but it is the only way we can get chains right now. The rolls weigh a ton! We are also building bikes from new frames that we can get, using components we have in old stock or parts the customer has from previous bikes. It is sort of what I imagine it was like during WWII when rationing was prevalent and you had to scrounge for everything!