I keep some long 3/8 tubes on hand for some of my castings and cut them with a bandsaw and true-up to the proper length using a barrel trimmer. Let me know if you do not find any closer or do not have some that you can cut to length yourself.
I have 3/8 tube in 10 in lengths, can you cut it to length? I could drop a short length in mail to you. Unfortunately even mailed tomorrow, it wont get to you until Monday.