Possible Mason Bee liners
For people who use disposable liners, these may work. The 8mm is extremely close to the 5/16 recommended size.
I would be tempted to just cut the straws in half and stuff them into some fat PVC pipes or a wooden box. We've had leafcutter bees build nests in an outdoor telephone, a BBQ pit, and an uncaulked crack between two walls.
Here is a link that might be useful: 8mm Paper straws (5/16 inch)