Here is a direct link to his Tai Chi for Arthritis series (there is a 35% discount until 12/31 for ALL DVDs, coupon code required but it's right there in the product description.) He has another site that focuses on related information, finding certified instructors, workshops (only 1 workshop per year in the US and Australia). Code only applies to actual DVD purchases, not the downloadable version. This is why I bought both Arthritis DVDs along with the intermediate 73 Sun Form DVD so I have something more challenging to move to once I've the first set of lessons down. Learning Tai Chi well, any style, isn't a fast process - which I like very much.
Amazon doesn't have the sales available through Dr Lam's TaiChi Productions site - and you can't even purchase his video lessons through Amazon, only the DVDs. How often is it more cost effective to NOT go through Amazon? I'm actually glad to see this as I prefer direct purchases if I can afford it whenever possible.