[url=http://www.kuehlprecisionfirearms.com/KPF%20.22%20upper%20M-4.htm]Kuehl Precision[/url] and [url=http://www.kurtskustomfirearms.citymax.com/catalog/item/29585/1131.htm]Kurt's Kustom[/url] both make M4 style uppers that use the Ciener kits for the bolt. 30-round mags are available (but really expensive). Kurt will weld steel aftermarket mag bodies onto the Ciener mags if you want. (20-round body on a 10-round Ciener, 30-round body on a 30-round Ciener.) Somebody here has posted pics of some with Termold bodies, but I don't know who did the work.
[url=http://www.cmmginc.com/inventory_a/uppers_tbl.html]CMMG[/url] has a DPMS M4 .22LR upper available. AFAIK only 10-round mags are available for it, and I don't know what they look like.
One of the conversion kits, I think the Army M261 kit, used 10-round mag inserts that fit into a USGI magazine. [url=http://www.compasslake.com/22uppers.htm]Compass Lake[/url] and [url=http://www.accuracyspeaks.com/22lrar15.htm]Accuracy Speaks[/url] make uppers that use the M261 kit, but they don't make M4 style uppers (just DCM practice uppers).