We sell 5-button vests made in one of nine Ettrick tweed patterns for $175 here:
http://giftshop.scottishtartans.org/tweed.html

Also, I really like the Ebay seller bookster1uk for a source of country tweed jackets and vests. Here is a direct link to the waistcoats they have currently listed, which at the moment all seem to be a size 38.

They have an actual store where you can purshase made-to-order goods, as well:
http://www.tweed-jacket.com/
Though the prices are obviously better on their Ebay items, the downside is you are limited to what they have listed. Again, here is a direct link to their waistcoats. Some really nice looking patterns available!