When I first started shooting Skeet 26 were very popular. In the first 20 years they became yesterdays news as 28, Metric 27&29 barrels gained a following. Then the 30 and 32 rage completed the 26 interest. A few went to 34 tubes sets but it soon came back to 30&32 for most shooters.
Today 26 12 gauge guns are hard to sell. Even 28 tube sets can be hard to sell but you might find an older fellow who will be happier for the lighter setup. Sporting Clays and Trap are where longer barrels shine. Another difficult sale is a four barrel Skeet gun. Tubes are what 99% of shooters want. Styles change, trends in shooting equipment are like fashions. Once out, they stay out for a long time.