Tormentor, it depends on the license given with the item. Without permission the copyright remains with the creator and it would be against the law to post the item even if it's unavailable elsewhere.
If the original zip file still has its 'readme' or 'copyright' text file that it came with, that should outline the usage and redistribution limitations, some items are available for unrestricted distribution. Or if you have the email for the creator you could write to them for permission to post the item. A lot of items are only unavailable because the creators have nowhere to host the item on line. Maybe you could make them an offer to host it here for a while
I have had a few third party items on a site of mine before with full permission of the creator. Most people are only too happy, if you ask first.
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