I can't agree more, buy a roll.
Good advice!
I would suggest measuring your windows to see how much you need, and then buy a single roll with at least that amount of window gasket. That quantity may be more than you want, but the problem with shorter lengths is you tend to have a lot of waste as you want one one length to do each window, not multiple pieces for a single window. Suppose you have four windows that need 14' long pieces each. That adds up to 56'. Two 25' lengths and a 10' wont work, a 50' and a 10' won't work either.
Unless they've changed policies, CR Laurence won't sell to "the unwashed masses", better known as individuals. You need to be a business, or at least you had to be when I tried to buy from them.
You can, however figure out the CR Laurence part number and then Google that. There will very likely be other companies that retail that same product. I've done that successfully.