>It’s very hard to near impossible to do or enforce all it takes is a country just by you that is willing to accept them.
You can set up treaties with your neighbors to enforce the same regulations. Also, if your country is sufficiently large enough, it's not really a concern because any savings from not having to follow the regulations will be wiped out by the increased cost in transporting the goods across the border.
You could also impose a tariff/charge on goods that transit through a neighboring country for no apparent reason (eg. China -> Mexico -> LA rather than China -> LA).
>People aren’t going to take a huge price hike
Source on the huge price hike? According to http://www.worldshipping.org/benefits-of-liner-shipping/glob..., the shipping industry contributes 183.3B to global GDP, and transports more than 4T worth of goods. Based on that, shipping accounts for approximately 4.5% of the cost of goods. Therefore, a 50% increase in cost because of emissions controls (very generous estimate) would only cause a 2.2% increase in the price of goods.
>and countries that are dependent on imports won’t ever enforce such requirements which would leave these vessels out there.
If it's announced years in advance, either shipping companies would adapt and get the vessels ready before the regulations take effect, or local manufacturers come online now that they're more competitive. No ships is ever going to be "stuck".