Here is a nice HobbyFix M16A4 model for sale that comes with a lot of extras like spare magazines.
The price was 278.000 JPY back in 2001 and it was made in limited numbers (approx 150).
https://page.auctions.yahoo.co.jp/jp/auction/j741097586It is a dummy model so it can not use plug fire caps, but it has a functional 3-round-burst fire control group. It is really heavy and realistic.
It was the last of the HF AR-15 series, that started 1991 with the M16A1, then there was a XM177E2 (1993), two runs of M4A1 (1999 and 2001) and the M16A4 (2001).
This is not my model and I do not know the seller, but I am just a big fan of the HobbyFix M16 series.