I don't know of anyone who carries 100mm 7075. If you need it fast, have a local shop (welding, marine fabrication) buy it for you from the local or regional distributor or buy it yourself if you can. Depending on where you live and luck it may take weeks to get what you want. If you have time check surplus metals and eBay.
May I ask why 7075? For a small quantity purchase it will be real expensive compared to 6061 ($60 vs $200-300) because it will be a special order. Also because it comes in a limited number of wall thickness, it is hard to achieve the theoretical weight savings in the real world. You just can't find the size you need and it ends up weighing as much as 6061.
If you are lucky enough to find what you need in stock or surplus or on eBay for a good price that is anouther story
I have been through this a couple of times in the last 2 years and ended up building carbon tubes
(NOTE: all this applies to small quantity, say two 2.5 meter beams. If you order a 1000', you can get what you want for only a little more than 6061)
