question about buying new wheels

[LuckyScott]

So I have a 1972 Suburban. Owned it over 25 years. Paint and interior is nice. Has a 4/6 Drop kit on it. Drives great, drive it everyday, Love it. My wife and I go to cruises and car shows with it, but it is not a show car, just a great daily driver.

Currently has a set of 15 inch corvette rally wheels and looks great. But I would like to update it with some nicer wheels.
I have been looking at some other trucks with nice 20 inch wheels and low profile tires and they look great.

It is not a bagged truck and not super low but it is lowered. I can put the Rally wheels on my 1970 truck. I usually just measure the backspacing and the width and buy used wheels and put them on myself. But the bigger wheels may be harder to fit and not really available used so I need to buy new.

How do I do it? Is there a special wheel shop I need to go to or can I use any wheel and tire shop?
I know once the tires are mounted I can't return them so I want to make sure I get the right size the first time.

Any advice?
I just love my C10 and want the wheels to look nice.