Hi there:
I do not remember the company name but might be able to find it in my files--IF they still exist. Clearly, the conversion biz for E150 vans is not what it was because there are no more half ton vans and very few conversions. I found them by looking on EBay but did the "buy it now" price and contacted the company directly. I just looked on EBay for Ford van seats and here is a 2013 set for $695 plus shipping:
Ford Econoline Van Gray Cloth Front Seats Manual O E M 97 13 | eBay
As I recall, I paid like $500 or $600 including shipping, circa 2005, so this price is kind of in line with that. Not cheap, but they are gonna last a long time and have predictable comfort. Mine are still fine after about 70k miles of use.
Good luck,
George