Your arms look good now in proportion to your body if you want more arm mass then you will simply have to grow your entire body. No sense in trying to put huge arms on that frame right now you need to concentrate on your entire physique imo. Larger back and deltas and chest and then my friend and only then will your arms fill out to match.

The only way to achieve what your wanting is synthol and thats a not a good option. Keep training hard and dieting you look good now OP you just want more mass so keep eatin and training and the large arms will soon follow.