don’t know if they are still around but there was a place just off J3 M4 on the western int market called robbies boxes,also at towcester the café on the A5,if you are near them of course,i made £50 pounds in 2 days a few years ago with euro pallets at robbies
Heading east on the A14, J41 (just before Bury St Edmunds) head up the slip road for the old Deputy Dogs Cafe, there’s a place buying pallets.