Earlier you posted a list of your existing customers. I would have thought that your "First Port of Call" would be to ask them what engines they have on their ships, and how many of each type, then at least you have a potential customer lined up already. You can also judge the relative number of engines of each type and hence the relative numbers of spares you should carry.
Then advertise on line,e.g. on the Diesel Duck's Trading Post, and email shipping companies to tell them that you have these parts in stock ready for shipping World Wide.
Each time you deal with a potential client, explain that you are willing to build up, and hold a stockpile of engine parts for them, according to their requirements, if they will help finance you. If you can get them to pay the price you pay from the scrapyard, up front, you only have to store them until you sell them, and then make your profit.
If I may say so, you are showing a lot of entrepreneurial promise, but you appear to be lacking something, Life skills? common sense? that make me wonder just how old you are.
It is always better to ask a stupid question than to do a stupid thing.