I bought the materials from a local fencing supplier, including all the gate hardware, except for the metal for the frame itself, which came from a local metal supplier (Metal Mart). Sorry, they don't have a "brand", or a part number that I could affiliate with an online part number for reference.
The brackets are really similar to these, though I paid less, and they're not exactly the same:
LinkThe metal poles are called a "tuff 40", but they're a higher quality steel schedule 40 pole (10.5').
For the attaching the boards to the gate frame, I first attached the horizontal stringers by directly bolting them to the metal frame. Drilled a hole all the way through the 2x4 and the steel, with the nut on the exposed side. The pickets are screwed on top like they would be traditionally. I think this is better than lags, personally. And with screws, I could take the picket off if I needed to access the bolt head. If you zoom in, you can make out where the bolt heads are on the left side of this picture on the 2x4's:
And on the back, you can see one of the nuts (not painted):
Supplier is TexMex -
https://texmexsupply.com/. They won't serve your area, but it could be worth a shot to call them and see who they buy from.