I'm not sure that's the right way to go about this. There are tons and tons of types of cheeses. I'm not sure you'll find a good list of all substitutes because it will be too big to put together.
Instead, I think you need to learn about the types of cheese so that you can make an informed decision. Is a cheese blue, sharp, creamy, hard, soft? How does it melt? What part of the world is it from? Those questions will allow you to find a cheese that is similar enough to make a good substitution.
For instance, if a recipe called for Pecorino a hard Italian cheese, Parmesan (another hard Italian cheese) would make a much better substitute than goat cheese or cheddar.
So see what cheeses are available at your local store. Write down the whole list (and preferably buy some of each). Get home and do a little bit of research on each one. Where is it from? How do people describe it? Take some notes on all of this. Then, when you see a new cheese in a recipe, look it up and see how it's described. Then find a cheese from a similar area with similar characteristics, and you should be good to go.
Edit: While I stand by my approach as a great way to go about this, I did find a good resource. Cook's Thesaurus has a great list of cheeses, including substitutes, broken down by type of cheese, type of milk, hardness, etc.
You may be able to find vegetarian Grana Padano style cheese, but I don't think you will find the real thing in vegetarian form.
This is because the making of Grana Padano is still a traditional process and true GP cheese is only produced in certain regions of Italy. It in fact has P.D.O. (Protected Designation of Origin) status, which means that only those cheeses produced in certain regions and using certain methods can legally be called Grana Padano. I imagine one of those methods is using animal rennet.
I would be surprised that there isn't some form of substitute available in Italy, as they have the highest proportion of vegetarians in Europe at 10%. I get the feeling, however, that they are perhaps less zealous about it than others if it means giving up good cheese.
The only suggestion I have found as an alternative to GP as something to sprinkle on pasta etc is nutritional yeast powder, which apparently has a similar nutty, creamy taste. Not ideal, but if you make the choice to be veggie you have to take the rough with the smooth!
I see from your profile that you live in the UK; we are lucky in that we have a lot of fantastic small local producers, so it may be worth looking up some local dairies or cheesemakers and seeing if they can offer an alternative.
Best Answer
I think your best bet might be to re-wax the cut surface with cheese wax, available from cheesemaking suppliers, and then store in the fridge, unless you have a cheese cave handy. In general a vertical halving will reduce storage loss by minimizing the cut surface - you could have had the same cheese availability by vertically halving the wheel (with a smaller cut surface) and then horizontally slicing the half you were using, opening it like a book if looking for the "whole round of cheese" look.
Your other best bet might be a bit too late, which is to be sure wedding one has paid for the whole cheese, and wedding two is prepared to pay for a whole cheese, so that if you open it up in 3 months and have a problem, the problem is only "smaller profit" not "taking a loss on trying to store cheese for 90 days after opening."
Linked item is just one I found as an example, not affiliated or even a customer.