I am assuming you want an absolute slick side. Model 1 Sales & Rock River Arms.
https://www.model1sales.com/index.cfm?fuseaction=category.display&category_id=415&CFID=4150548&CFTOKEN=ee999da331fa6167-FC13E73B-D48E-6F6B-A9713F41E12D60D2&jsessionid=DF481FC08765CAD00938C71AFD511527.cfusion
https://www.rockriverarms.com/index.cfm?fuseaction=category.display&category_id=242&CFID=609669580&CFTOKEN=83111733
I know Colt dos them too, but they are harder to find. I know Aero also does one with no forward assist, but it has the brass deflector nipple sticking out.
http://www.avantlink.com/click.php?tt=cl&pw=55963&ctc=j40djqcudb00zk8a02gtd&mi=13601&url=https%3A%2F%2Faeroprecisionusa.com%2Far15-stripped-upper-receiver-no-fa.html
Then there are a couple billet styles without, but I don't recall them offhand. I went with the Model 1 and it matched up excellent with my Black Creek Lower, and for a couple extra bucks they swapped the 9mm port door assembly for a standard. Hope that helps!