JustPete

Ohio Travel Bag seems to have a nice selection and may have what you're looking for. I don't use tubular rivets, so I can't speak on their quality, but the other items I've ordered from here have always been good. Ohio travel bag https://ohiotravelbag.com/collections/rivets

Sent DM

I also have a 4800 Pro and am very happy with it- although I don't have much to compare it to since its the only machine I've used! I have been running mostly 138 top and bottom though with no problems- it seems to really like this in the 12-15oz. range, which works great for me. I also have run some 207 at closer to 22-24 oz., and while it took some fiddling, I was able to get some good results making adjustments mostly on intuition. I like the EPS, but again I've never used a machine without one, so that may not be something you're keen on if you're not used to it. The laser guide seems to be unnecessary to me, but it may show its strength some day. I also feel the 3 presser feet and 8 bobbins included in the pro package along with the other tools and extra needles and thread will get me pretty far without having to order a bunch of other stuff right away. I've contacted Techsew twice and they've been nothing but helpful both times. I did have an issue with my bobbin winder not being set up right, but my problem was solved quickly with just a few helpful emails. And I am in Ohio and received my machine about a week and a half after I ordered it, if that tells you anything... I did pay for the lift gate service since I have a pretty long driveway and the driver was able to just drop it in my truck and I was good to go! Not sure if that helps or not but I just thought I'd share my experience!

Acadia Leather https://www.acadialeather.com/ has some nice options too, at a sometimes far more affordable price- especially if you take advantage of their frequent sales. They don't cut sides down, though last I knew, so it's all or nothing- but the shipping is free in the U.S.! The Harvest line has a nice oily feel to it with a lot of pull-up, but still a harder waxier finish, as you mentioned you like

In my experience, it's been just as much the angle of my hammer strikes as it is the angle of the irons. A calculated, direct down blow drives the chisels right where I've positioned them leaving a straight and true stitching hole- any variance in angle produces an equally offset stitching hole. This observation really helped my son straighten out his lines on both the front and the back of his pieces.