I make mine out of 1/2" MDF and put a piece of Formica on it.
It fits my Delta perfect that way. Just trace out your existing insert and cut a new one.

I used my table saw to cut the piece to length and width.
When I didn’t have a band saw, I used my hand held scroll saw to cut the round ends and finished them with a hand held angle grinder. It fit really well.

Just lower the blade all of the way, put in insert in place, move fence over insert to help hold it down making sure that the blade wont come up through the fence. Then turn on saw and use a scrap to put some downward force on the insert and slowly crank the blade up through the insert.

To make additional inserts I cut a bunch of pieces of 1/2" MDF to length and width.
I then screwed my first homemade insert to my work bench.
Then screwed a blank on top of my first insert and used a router with a flush trimmer bit to duplicate the first one.
I made several of them.
One for each stacked dado size and one for my standard table saw blades and one for my narrow kerf blades and a few extra's laying around. They will come in handy if I butcher up one of the good ones.

I always use the zero clearance insert on my table saw. It eliminates jams, reduces kickbacks and allows me to cut fine slices of veneer off the side of solid stock. This veneer would otherwise be sucked down under the table. Oh, and BTW, you might need to cut some veneer to glue under the insert to get the right height.
I never use the original factory insert...NEVER.

These are teak doors that I made for my boat. They were made with pretty much a minimum of tools but turned out just fine for me. It just takes longer.

Two writing tables that I built for step-daughter and step-son's future wife. They are constructed from Red Oak and African Padouk. Pretty much the only tools used were a tablesaw, bandsaw, drill press, router, electric sander, skil saw, hand sander and cabinet scraper