And then...
Go here
Ronco Plastics to find a new tank. They make TOP quality plastic tanks for a very reasonable price and have more than 400 shapes and sizes, including over 100 non-rectangular...and they install fittings in the sizes and locations specified by the customer when they make the tank.
If your hoses are more than 10 years old, you should also replace those...and depending upon the make/model/age of your toilet, it's almost certain to be overdue for maintenance, if not replacement, too.
So before you do anything, I suggest you spend some time in the HeadMistress forum reading the discussions about replacing toilets, tanks and hoses to end up with a trouble-free, odor-free system...or you can just check out the link in my signature below.
And the good news is, you can get everything you need including the tank from the online store on this site. Not only are their prices much better than you're likely to find anywhere else, but when you buy from here you help to support the site.
sbo.com plumbing