(I hit Submit too early, LOL).
These guys that Cameron recommended (in Oregon) have great stuff.
http://www.stuewe.com/products/treepots.php
Their deepest seedling pot is 16 inches, which is perfect.
Would
save you from one complete up=potting, but then the NEXT pot size up would be a 5 gallon

because a 2 gallon pot is only just 9 inches tall.
BUT:
Since 2 gallon pots are only 23 cm 9 inches, I'd recommend (for next year's up-potting), you use what I did.
Cheaper than borscht, sometimes FREE.
These 25 cm (10 inches tall) "florist fresh flower black pots"...just drill one big drain hole in the bottom of each.
Your Safeway florist probably has 500 of those black pots she's trying to get rid of.
Good person to get to know.
I know putting a seedling with 16 inch roots into a 10 inch tall (FREE MAYBE) florist pot sounds like a math impossibility, but you can gently angle/bend the root area.
Here's my seedlings from 10 inch slurp cups with a "florist black pot" beside it.
<a href="
http://www.flickr.com/photos/southslope/5353157517/" title="DSC04283 by edible_plum, on Flickr"><img src="
http://farm6.staticflickr.com/5209/5353 ... c7fc_z.jpg" width="640" height="480" alt="DSC04283"></a>
Bet someone would pay $15.00 for a palm in that black pot (versus a seedling pot).
The one real risk in using those florist pots for 1 year old seedlings is there's a lot of soil.
So to prevent root rot, use the grittiest gravelly soil mix you can find so it drains really really well.
I'd recommend a soil mix with NO peat moss/NO sand at all.
Here's my palm roots:
<a href="
http://www.flickr.com/photos/southslope/2887935769/" title="DSC01690 by edible_plum, on Flickr"><img src="
http://farm4.staticflickr.com/3204/2887 ... c88d_z.jpg" width="480" height="640" alt="DSC01690"></a>
That's why palm pots are always much deeper (or should be) than wide:
<a href="
http://www.flickr.com/photos/southslope/2187822251/" title="DSC00819 by edible_plum, on Flickr"><img src="
http://farm3.staticflickr.com/2352/2187 ... 8cb0_z.jpg" width="640" height="480" alt="DSC00819"></a>
...plus you can plan your website during winter.
As though your honey-do list isn't long enough already.
Barb