The theory behind this method is that people will be trying to scrape for "blog not found" or whatever the exact phrases are for Tumblr and Blogspot and you want to beat them to it. So instead we are just going to assume that a certain percentage at any given time is deleted. Which is true of course. And then we are just going to scrape like hell and test each site against something - in this case we are looking for 404'ed sites since the deleted sites return that status code.

Using this method you will find way more deleted blogs with PR or PA. Also, it's quite easy

(This is all done in Scrapebox)

So just scrape up some blogs using site:tumblr.com (or blogspot.com)

Aim for 100k to start if you want to end up with a decent amount to work with.

Now trim to root and remove dupes.

Open up the alive checker and go check everything against a 200 status code (which is default) and save off the dead blogs. For some reason I found this to be better than just checking against 404 codes but you can do that as well. If you do that then you will want to save the alive blogs since Scrapebox will consider the results of the entered code to be "alive". It's really more of a success test and not an alive one.

You won't be able to page scan these as they will just return a 404 status code and you will get an error.

PR check or check page authority.

You can make your own program to check from here but such a high number of these will be deleted you can just do it manually as well as you go and create the blogs. If you have the ability to code something up for it then I don't really need to tell you what to do.
The Blogspots are going to be stronger overall - I would check the PA since you're going to have several results to choose from.