I have seen only DSM2 compatible micro receivers.
How about 0.23 grams (0.008 oz) without ESC or 0,27 grams (0.0095 oz) inclusive ESC ;-) http://www.micronradiocontrol.co.uk/rx_dt.html
You will also find a TX module on the bottom of the page.
What kind of electronics do you find in a champ?
Do they use the bric with servos on it, then it will be a challenge to get a replacement.
You can probaly find a crasched Parkzone ultra micro as a spare part supply for a few dollars.