Hi there
Like you, we just sold the odd add-on foil balloon but my daughter was very interested in learning how to make balloon arches etc. She found that the best website was Qualatex and that they do a Balloon Design Artist course via DVD. You pay a sum and get three DVD's which you watch and take notes and then take three tests, one after each DVD, online. Once you have passed them you can go forward and take a practical exam to gain your CBA.
She has just passed the first part and has already had a couple of orders - one a wedding - which have proved quite lucrative.

Hope this helps.

Kind regards
Heather - LilyLady