Fields for encoding ISRC and barcodes

I am wishing to encode mp3 files of single song tracks for sale in virtual worlds, such as Second Life, and also for playing on internet radio. I would like to encode both ISRC and barcode numbers in the id3 tag v2.3

I had been using LAME within Cakewalk's SONAR 7 but the only way I can get the copyright and product codes into the tag is in the 'Comments' field there. I have looked to Mp3tag v2.4 to address this problem but I can't see how I can. Could anyone provide helpful suggestions or comments on this issue? Thanx.

To enter ISRC number, select a file, press Alt+t and create a new tag field ISRC

You could do the same for barcode, but it has no official tag/frame
See Mp3tag help chapter "Names and mapping of ID3v2/WMA tag fields" and