I've purchased 3 scripts in the past, apslayer, extreme fletching and extreme hunter. They are now removed from the SDN and no longer being worked on.... Is there anything I can do to trade them for different hunter/fletching scripts?

Purchase new ones

Unfortunately I don't think this is possible. When you purchase a script, you own it for the lifetime of the script - these scripts were removed quite some time ago ):

Hopefully you got your moneys worth while they were still active! 

-Apa

This happens in every single botting community. Some older scripts stop being supported, most likely because the script's generally unpopular and/or the original scriptwriter has left.

Two of the scripts you've mentioned were created by @Extreme Scripts who is banned. In some circumstances where a script is actually worth keeping, another scriptwriter (or even developer) takes up the task to maintain it. This doesn't appear to have been the case because those scripts aren't available on the SDN anymore.

One possible reason I suspect is that there is no standard scriptwriters adhere to, so our scripts literally come in all shapes and sizes, so just picking up someone else's script and trying to learn what they did can be a hell of a task in itself.

This is one of many reasons why you should write your own scripts.

As @Apaec has said, hopefully you got your money worth.