Howdy, Im happy you asked.
This is my first post, and am excited to use it to help someone.
My answer isnt how to get one, its how to make one (free option).
I own a Sunbeam EM4800C. I had the exact same qusetion about 1 month ago after a long session on this website.
I too wanted a non pressurised basket for my machine, but due to being a tight arse and not wanting to spend money or drive to a spare parts shop to ask, I took the "home modification" option.
I have read posts from others that used angle grinders to cut the bottom of their baskets, but with less than 1mm or so clearance between the two floors, there was too much risk of hitting the top floor and destroying the basket all together.
My father owns a metal lathe, this was the only thing I could think of to do the job with precision.
The initial cut I did was a test run, only cutting to the outside of the dimples on the bottom. Boy, there was some crap trapped in there.
I took the basket back home and tested the mod.
After some grind & tamp alterations, I was very impressed. :D
So, next trip to my parents house I was turning the rest of the basket floor off. BUT you must leave a lip around the edge to hold the other floor in!!!
My mod left about 5mm round the edge, which clears all the holes but keeps the basket strong.
The Sunbeam baskets have larger holes in the floor than other non pressurised baskets so suitable grind & tamp combinations may take a while to master.
I also removed the plastic floor from the PF handle to remove any chances of sludge build up.
Also pix attached of a friends effort of a "Naked PortaFilter." Using a 44mm holesaw as specified in another thread on this fantasic forum.
I recommend doing this with a spare handle only as there are some downsides of being naked.
Also, if you havnt got a burr grinder, get one.
So, in closing, find someone with a metal lathe. It will take them 2-3 mins and im sure they would be happy to help.
Hope my ranting helped.