jtb - despite a reputation for spreading fast enough to eat the whole neighborhood, based on my experience you should expect it to take 3 years for bamboo to provide the screen you seek. i would suggest that you get 8 nice divisions and plant them on 4 foot centers to cover 30 feet. you can use more and plant on tighter centers to try to create the instant screen if you are allowed to dig enough and wish to put out the effort. you could even dig a 30 foot trench and put the roootballs in abutting each other for a decent screen but each division will require about 2-3 years to store up enough energy reserves to begin producing canes the size of the ones that you originally dig and to fill the gaps in between. in year 3 it will take off and you should have a nice screen even if you started on 4 foot centers.

the advantage to getting it locally is that you should be able to know if it is hardy enough to stay evergreen. do not wait until it sprouts to dig, that is a bad idea, rather dig just before it should beging sprouting, probably mid-march in your area. dig from the outer edge of the grove and be sure to get large rootballs. others may weigh in here with their digging tips, the important things are digging from the outer edge of the grove, getting rootballs of an appropriate size (my guide is to maintain a rootball size equal to 8 times the diameter of the canes, all the way around the canes. in other words if you dig a single cane division of a 1 inch diameter cane, make sure that the rootball is at least 8 inches away from the cane on all sides, translating roughly into a 16 inch diameter rootball for a 1 inch cane), dig on an overcast day if possible, keep the rootball moist and do not leave the foliage exposed on the drive home, wrap it up well.

Also, the bigger diameter culm you can get the better and faster it will grow. I got via mail order a cheap size (TINY!) of some timber bamboo (P. Vivax) and it was so puny it died after the first winter. If you have to dig the bamboo yourself, I found the easiest way to do it is, get some hand pruner, and when you hit an underground running root, clip it with the pruner. The first time I dug bamboo it took me a half hour to slice through it with a shovel. With a pruner it's snipped in no time. May want to look for some bisetti, it is a fast grower I hear. Also makes a good screen too. Good luck!