I've read this post a lot,
Good for you to figure out other years that will interchange.
Your lower unit is out there, your going to have to search hard to find it.
Try ebay first, then craigs list, run a add for every city in your state, then start trying all out states. Yes" its a lot of work to have fun"
Never give up, or buy a used four stroke.
Wait, whats wrong with your lower unit?
If your boating season is over you have months to fix this.