I think it's time you gave up and just get some-one to do it for you!
You have all the information necessary for dealing with it one way or another. Fitting plastic air bricks or some other grill on the end of the vent ducts is the least of your problems.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local