I spent a few months looking for a drilled tank, they seem to be in very short supply these days.
But after years of procrastination, I did finally drill my first tank this year, it was so much easier than I ever thought it would be, and I am not a DIY guy at all.
EDIT: But there are other options available to you"
1-Some LFS's will drill it for you at a small price, like $25 per hole for example. The problem is that you need to bring the tank to them and then bring it back to your place, which is added risk to move the tank so much. And of course there is no guarantee.
2-If you live in a city with an online reef club of some sort, you can ask if someone is able to drill it for you. Most of us are nice and very happy to help each other if possible
You may have some trouble finding a predrilled aquarium with your exact specifications, unless you are looking a packaged system such as Red Sea, waterbox, etc.
As others stated, drilling a tank is super easy. The only tanks that ever gave me trouble were the 10 gallon because the glass was so thin. The larger the tank, the easier to drill IMO. Just takes a little longer. The diamond hole saws are super cheap and you can use a really cheap drill.
Drilling isn't difficult but maybe consider a hob overflow if you do not want to drill. I've been running two hob overflows on the 180g in my aquarium showcase for almost 8 years and used to have a 150g sharing the basement sump that also ran with a hob. Contrary to what many people say if they are set up properly they never loose syphon and never cause a flood.
Alternatively, I am sure that you can find a glass shop local to you who can be persuaded in helping out with the drilling if you're not comfortable doing it yourself.
It is a daunting task, I bought a couple of pieces of glass of similar thickness to practice on.