How many holes does the tank have? Hopefully 2-3.
Get a tape measure and measure the size of the hole. From there you can figure out what size bulkhead to buy.
If you want it asap the stores around us will usually have the bulkhead in stock (Xtreme Marine or Aquatic Reef Design). If they don't have it then for sure Tat Aquatics in TO will have it, he generally has a lot of sizes of bulkheads.
If not you can always order from Amazon or Marinedepot.