The reason you don't see a lot of khukuri past the 20" mark is because they consume a lot of coal at the forge. Prices of fuel and supplies have steadily risen over the last few years and since the very large khukuri are somewhat of a niche market is was decided that it was more cost effective to stay with making the bread and butter lengths and models and some swords. Auntie may still take special orders for larger khukuri, but you'd have to ask her.