Seriously brother - have you even looked around??
Parts kits are in short supply on hand, but everyone sells a parts kit, or a full upper, in the configuration you are talking about.
Rock River Arms
Want high end for the sake of paying a ton of money for name?
Brownell's has parts kits for the lower and BCG for the Upper. I believe they even sell completed uppers....
Take a stroll through the AR-15 section of this forum - there are a TON of threads about what people bought, where they got it, why they went that route. There is probably more information already in those threads than you can digest in a week of reading....