I went ahead and ordered the part through GitzoSpares.com . I was trying to find a US source, but GitzoSpares (UK based) was price competitive and shipping was reasonable. I took expedited shipping rather than free shipping to get it faster.
Kind of irritating to have to buy the full upper leg section since it cost $151.00 including shipping. I'd love to find a broken 3540/3541 or even a 3530 to use for parts. I have two 3540LS tripods.
For the record, I contacted all the following companies and went to my personal contact:
Bogen/Manfrotto - Gitzo distributor in the US Adorama B&H KEH Berger Brothers Hunt's LensRentals.com eBay
All of them were helpful - but none of them stocked parts or retained popular broken tripods. Several offered to contact their rep for assistance. And Bogen Manfrotto was out of stock on the part with a 2 month backorder - and I know someone who has been waiting 2 months on a similar part.
Helen Oster at Adorama was the most helpful. Her rep explained that the factory in Italy is closed for Holiday until the end of August. After that time, order normally take 4 weeks. That puts me at the end of September best case. So I definitely need a plan B.