Many times I used a chisel to cut off a hard-to-reach piece of lumber, I was wishing I had an adequate blade for my 4.5" grinder, as I don't own an oscillating tool. Why is it hard to find? Is it because they would be dangerous?
They are made, they look like mini chainsaws and are commonly used for carving bowls.
A common brand for these blades is Lancelot
You can also get smaller saw blades in the 4.5" form factor. I suggest you go to a saw store or woodworking shop. Here is a product on Amazon:
The primary reason is grinders typically spin at 10,000 rpm. Wood cutting saws typically spin in the 3500 to 4000 rpm. If you spun a typical circular saw blade at 10,000 rpm it would come apart. As @Matthew PK has shown they make wheels for working wood with a grinder but they are not the typical toothed blades.
I have an old Makita mini grinder that my dad out fitted with a 5" wood cutting blade from a mini circular saw. Unfortunately it has no guard and no handle. We use it for hard to reach areas that a regular circ saw or reciprocating saw won't reach. But my dad and I have nick named it the "killer" because it is the scariest tool I've ever used. if you're making a deep cut in wood and it catches because you twisted the blade, it kicks out uncontrollably. I agree with the guy from Down Under, a mini grinder with a wood cutting blade is recipe for disaster. That's the most logical reason why they don't make a wood cutting blade for a mini grinder, due to the high speed of the blade.
Just use the chain saw type 4 inch blade shown above. They fit in the grinder perfectly, still have the advantage of the safety guard to protect you and have the added advantage of the guard deflecting the chips away from your face. I use them all the time and have done so for about ten years. You sharpen them like a chain saw with a file right on site if you like and the chains are replaceable when ever you want. I have a milwaukee 5 inch cordless grinder that runs it great and it will cut through a 2x6 in about 30 seconds. It is the tool made for the job unlike the jerry rigging ideas presented by some and costs less. Amazon has them for $15-40. Home depot sells them for a little more in the tool area too. A plate or biscuit jointer blade costs that much or more sometimes.
I was ready to buy a wood blade for my grinder, I sometimes see good pieces of lumber in garbage bins here in NY and often would like a cordless tool to make a quick cut just in case the piece of wood I encounter is too long to fit in my corolla and the only cordless cutting tool I have is a grinder, however after reading the posts and getting an understanding of the danger of using such a blade on a grinder, I changed my mind. I don't have a lot of experience in this field but maybe just to do a quick cut on wood left in the trash maybe the standard grinder blade will do