There is only one other vendor I found in the Czech Republic in addition to Extrem Textil in Germany, which has an excellent silpoly, a little heavier than the US offerings, and suggested by some on these forums to be of higher quality. There have been some problems with ET sales outside Germany, but the facts change and you should check their website. As far as the US is concerned, there was a long hiatus after the pandemic arrived; but more recently I’ve had no difficulty with ET shipments to the US.
As far as sewing feet are concerned, I tailor and pin fabrics before sewing so might be regarded as in the dark ages and certainly not looking to automate just to make a few tents. Nor do I try to develop fabric panel shapes on the computer, as different fabrics drape differently and depend on how the grain on panels is oriented. There are different approaches to such orientation expressed on these forums by Dan Durston and others. There is a recent comment by Henry S that raises new issues for me, but it has been a simple matter to visit large gear stores and look at tents to see how grains and panels are oriented. Once fabric panels are tailored and the seams pinned up, there is much less guesswork, so almost no need to seam rip and do over to arrive at a taut tent canopy, and far less concern with, say, sewing a backpack. So leave others to their own devices.
In case you’re interested, or might benefit from illustration, here is a photo of a the rear netting being pinned up while modifying an inner tent:
