The only company I am aware (there may be more of course) who do these pellets, is Marriages. Unfortunately, they are southern based, and most local place who stock them to me, was Wales!!
I rang up and they were very good, and sent me 4 bags next day delivery - all double bagged so no split bags as they came by courier van. You can order as much or little as you want, so may worth looking on line and ordering, if you can find someone to share. I did ask about the likelyhood of them stocking this medicated feed in Northern areas, and they said it was a possibility.
I would gladly let you have some of mine, as I have more than enough, but Derbyshire and Fife are not really local to one another, are they?!!
I have always used the big tubs of wormer and mixed it myself, but now no longer allowed to do this. Anyway, the pellets are much easier to use, and no mixing involved. And price wise, including delivery, it worked out no more than buying the pellets and powder and mixing it.
Apparantly, with the number of hens, they worked out I would need 5 bags to cover the hens for a week!!! Think thats 1kg per hen per week, so if you have 20 hens, you must be using a bag a week (I certainly do not use 5 bags!)