Greetings Treliss,
I attempted to locate this bag for you from Craftsman - Not available, Parts Warehouse - Not available as well as about 5 or 6 additional parts houses. It would appear this bag has from what I can tell been discontinued. MTD shows it as discontinued.
I resorted to locating the actual part number which is 580947303 and then doing a widespread search of the internet locate some used bags that would fit the 917.370413 machine.
Results:
* [link|https://www.ebay.com/itm/325931754519?itmmeta=01HTGNY1QG4YWH6DA9J0ATZ664&hash=item4be30be417:g:BrgAAOSwsgpldHd4&itmprp=enc%3AAQAJAAAA8CTLyusGTMTZWsoyrkhGBvCsaJu1PckoOa8hXRUiLjkltboD22%2Fd--9216gAG2FLRe05Jn0IcQcmAcd86njz9o%2B1%2FrVIXcq2ZjJ2TSplhnX4ul3P2nnTJL8IGLiTAXPicsGzTpUgmRGetHp0741l6UMzG3oJsWKkUVz364JpBOMbmim05FUykzQ%2Fcja7AtPPm20RwqEx7t%2BjjG4qDT04bUKtqoNl%2BIrBxMRulJDk2BDA%2BfrgNJ56Mk2Rb2kWBhyRu00qab0Qv0xvp6H3VCk7lM9PvmJymONgyREP%2Biwl%2F9LVi8DIx3%2Fk1wGEXIv%2B7gYknw%3D%3D%7Ctkp%3ABk9SR-ab-JXUYw|Ebay Option|new_window=true] 1
* [link|https://www.ebay.com/itm/355007034253?itmmeta=01HTGPAHJH11PZ8QW3H55EZ9H3&hash=item52a811738d:g:aksAAOSwQxRk7jp~&itmprp=enc%3AAQAJAAAA8Iktx1D%2Bqw9V1ZUJkUvAR8EK00KGA7rSPMhojjVQsCEDDr0s9UDc0JLtngcUYMJNGdddjwHABccdc1XMBeU3kXcKlhe1Wm3sN1d2pWbJSxHYfSEA7WcFXY4g%2F3%2BOB0vBbiU0i4qSMabIzbDeMcu0DvqtqEuNe8cSwz4u1JSWWRwhXOscPg2eHomREygNnaH4OsDiH%2BWIR3yX3NAcD51dKnvXxx0F0KTh2SBQsRyeLgieBvMZFe91azU8mgXRXAG77okdylN0WZ3m6aUEERSh3AivBpsi6fLILWk%2FzK3HQygq15kVFnPc56mf9P7VM8DxEA%3D%3D%7Ctkp%3ABk9SR7iZqpbUYw|Ebay Option 2|new_window=true]
I hope this helps you out.
Cheers!
Monte