Are steel hidden inserts available for carbon shafts? If YES, please identify vendors.

Are different length inserts available? If YES, please identify vendors of longer inserts.

Not steel, but brass. Kustom King and 3 rivers sells them. Shawn

They are 75gr. brass inserts. Easy way to add weight up front. Then if you want more weight get the weight system from Sipsey Archery Supplies. They are 20gr or 50gr weights that screw into the back of the insert, inside the shaft.

Cabelas also has the 100 gr. brass inserts for the Axis shafts.  Jr.

check out Muzzy's selection, Mark (Land) has done more playing around and R & D with carbon arrows and inserts than anyone i know---i believe they offer 50 and 100 grain inserts for regular carbons and HIT (Axis, MX and FMJ) system arrows. i've used the regular carbon size in both 50 and 100 grain quite a bit and found them to be very uniform in weight and dimensions. He's also a good source of information about carbon arrows with regards to length/point weight/insert weight, etc.