I'm starting to make my 2nd birch bark canoe and would like logs of 5ft lengths for the ribs - usually red cedar. And for the sheathing, white cedar. And if they got'em, I'll be looking or longer logs - say 15ft to make the gunwhales.
OK, What you're looking for is Northern White Cedar (Thuja occidentalis). Start looking in the direction of Log Home Builders, Cedar Fence suppliers and cedar shingle manufacturers. Since the narrow diameter is what you're looking for, it should not be a problem finding what you need since each of these are looking for someting in greater diameter than you are. If you can't get logs directly from them, ask them to reveal thier sources as those folks are generally going to be looking for ways to get rid of this small diameter material, too. Keep asking. A guy who knows a guy, who knows a guy, etc. is probably how it will happen. a.k.a. networking. www.whitecedarshingles.com might be a place to start.
Good Luck, Splinter