specific/rare food allergies are such misery, i feel your struggle. Although they're not specifically Chinese, i know Mai Thai Restaurant does large and small-scale catering, and from the website it seems like they're flexible about food requirements. Best of luck on your quest!

You could also get a bunch of friends together and work together to make tons. Make it a fun occasion and send them home with a few as compensation? Extra fun if you have lots of onion allergy buddies.