I may be wrong or missing something important, but I'm going to say it again: scarcity of Alden shell is a function of Alden being in demand beyond Alden's capacity to produce. You can go to several other makers, all sourcing shell from Horween, and get something immediately or MTO within a month or so and in an array of shell colors.
I am not so sure that this is true. I recently contacted Mitchell Leather about a wallet in shell cordovan (any color besides black) and Dave mentioned that not only did he not have any, but he didn't know when he would receive more.
This is obviously one data point and he could be allocating what he does get from them to their briefcases, but I think Horween Shell Cordovan is in tight supply also.