I have a 6' wide trailer, and I bought load bars for it about 5 years ago. I just got the regular length bars, drilled out the original pins, and cut the square tubing down with an abrasive saw. I then drilled new holes, and instead of a pin I used 3/8" flat head machine screws, with a coupling nut in the center to keep the end pieces in place. I must have used Loctite on them, because they're still going strong 5 years later.
If I remember right, I had to order the machine screws from Fastenal because my local hardware store didn't have what I needed, but in the end it was cheap, not terrible difficult, and very effective.
