I'm looking to download the full pruned blockchain for Monero instead of syncing it and then pruning it. Where can I find this pruned monero blockchain file?
It helps to better understand first how pruning works.
When pruning, your blockchain gets split into stripes. These start from a random point chosen when you first decide to prune. If you are pruning, only your pruning stripes get pruned (non-essential data gets removed after validation). The non-pruning stripes will have full data. So every node that prunes, their stripes of unpruned data will be different to other pruned nodes, based on the random starting point mentioned earlier. Your pruned node still participates on the network sharing blocks to other nodes that need to sync - but you are obviously only able to share blocks that you have not pruned.
Armed with this information, you can see it would be extremely harmful to the network if every node had the exact same stripes of pruned/unpruned data. This is why it makes no sense to have a pruned blockchain file available for downloading.
Also, when you run a node, you want your node to have fully validated every block. A pruned node still does this - it only prunes data for blocks that fall into a pruned stripe after it has validated it. This is another reason why you wouldn't want to download a pruned blockchain file - you'd have no way to validate it.
I'll also add, the full blockchain.raw download file is pretty much redundant nowadays anyway. The syncing speed of the blockchain directly from the daemon, on the network, has been greatly improved over the years.
To wrap up, if you wish to run a pruned node, start the daemon with
--prune-blockchain. It will download and validate every block from the network but not save everything to disk. It will continue to participate on the network in sharing blocks it has not pruned to other nodes.