I get sleeves at Grizzly.    https://www.grizzly.com/products/grizzly-1-1-2-dia.-x-5-1-2-hard-sanding-sleeve-a80-3-pk./h6670

Look around, they have several sizes, but they are not organized very well.

They also have longer sleeves that could be cut down. 
Yeah, BusyBee is the equivalent up here in Canada but they don't carry them anymore. I have a bag full of 150 grit but will look for a bit longer before I pay the shipping.

Darrel