I assume you are talking about the lower block of the mainsheet? I have3 been sailing for over 55 years and never heard of a "mainsheet controller". Anyway, There are several brands to check out, Garhauer, Schaefer, Harken, just to name 3. My advice though, would be to give Rudy Nickerson at D&R Marine a call, (508) 544-3001, he was the Parts Dept. guy at O'DAY and now runs a little shop supplying parts for our O'DAY boats. He is on-line,
www.drmarine.com, but a phone call gets more info. The 22 and 23 used basically the same mainsheet rigging, so here is a drawing of the 22/23 mainsheet.