I need size 22 but longer than the standard 24" so I can tuck it into my pants better. Anybody know someone who makes them custom? The ones I found online only make it in cotton. Thanks!
The following is based on my experience buying Chabad-style Tallit Katan in Crown Heights. Your mileage may vary.
The sizes of Tzitzit, 22, 24, etc. is a measurement, in inches, of the width of the Tallit Katan.
In my experience, until about 10 years ago, a size 22 tzitzit had 22 inches widthwise, and was also 22 inches from the neck to the bottom of the garment.
Recently, most Tallit Katans I've found for sale measure 22 inches from the almost top of the shoulders to the bottom of the garment. This means that the garment is less than 22 inches from the neck to the bottom of the garment.
So, see if you can find a size 24 of one of the old-style garments (that measures from neck to bottom), and it will be longer than the new-style garments. [It is very likely that the Tzitzit in the Eichler's Wizard - mentioned here - are this style of Tallit Katan, because they measure 22 inches wide by 26 inches long]
If it helps, here's a picture of the label of the last Tallit Katan I purchased, it measures 24 inches from the shoulder.