Long dremel bits, where to buy?

These are inch and 3/4 OAL.

Goxawee 20pcs Diamond Burr Set Rotary Grinding Drill Bits Set for Dremel Tool | eBay

And I would suggest this:

Flexible Dremel Extension Shaft long moto attachment chuck Rotary Tool accessory | eBay

IF you don't have one. I have one of these, and I sometimes put it on, hang the Dremel over the work area and use the extension.