Filestube like 4Shared, Deposit Files, MegaShares etc. etc. etc. are used by people genuinely sharing files they own and a massive storage facility for pirated goods.
As regards the Iowa model, I think the only ones that were available are GPM 61 and JSC 97. Both of which "may" be available for purchase from reputable sites that have permission, or if you're lucky from a collector on EBay (be aware though that some of the ebay models are scans.) I honestly don't know if the GPM or JSC models are available currently from the original distributors as they're fairly old models. I think - can't confirm I'm afraid - but I think the JSC was a waterline model and the GPM was full hull.
If either of these are available for download somewhere like Filestube, I would suggest they are more than likely pirated scans, not originals.