Correct.
There are options.
This is what I got. I'll only give it a lukewarm endorsement. It works great, but was an incredibly tight fit into the adapter holder (use one of the 4 adapters that came with the machine). Stay with one that reviews say fit the 4 - there are many where the ring portion is too tall and will fit the 3 but not the 4's adapter.
https://www.amazon.com/dp/B07D838BHJ
Second option is to use the Cricut/Roland style blade holders that it sounds like you already have. ...I've found some 3d print files of adapters for those holders to cameo 4 that I'm eventually going to get made and try too. (I just found this - did some research and the design I previously downloaded is no longer posted on the site)
https://www.thingiverse.com/thing:4283714
This one? EVISWIY Blade CB09 for Silhouette Graphtec Holder with 15psc Vinyl Fabric Cutting Blades (30/45/60 Degree) for Silhouette Cameo 1 2 3/Portrait/Curio/Graphtec 6000/CE 5000-60 Plotter https://www.amazon.com/dp/B07D838BHJ/ref=cm_sw_r_cp_api_glc_fabc_3so9FbFA131XV
This is the blade holder I use with my cameo 4 machine. I bought a backup holder off Amazon, and was super disappointed with the quality, and ended up buying a 2nd one of those holders.
I originally bought one of the blades from the same place, but they are somewhat pricey. So the next time I bought some blades, it was off Amazon in the bundle packs.
The blades come in 3 different angels: 30,45,60 degrees. They are used for different types of materials. I used the 60 degree blade for vinyl because the thin point helps with small details. I use the 30/45 degree for thicker card stock.
This is the pack of blades I bought. It comes with a holder, but this was the one that was very cheap quality compared to the other. I just bought it for the blades.
So last year I bought a cameo 3 used off a friend for $100. This is basically the same as a cricut that your mom or wife possibly owns. I'm currently running a cb09 blade from amazon with the 30 degree blade. I then purchased this $10 pen holder and put a fabric pen in it.
I have my cb09 blade set to force 28, speed 5, passes 3. Blade depth has to be set manually, and I have the blade pretty far out there.
I have my pen set to force 18, speed 10, passes 1.
This is all for 500d nylon. As you might expect, there is not a ton of information out there for using these craft machines for cutting tactical nylon. Hopefully finds this helpful down the road.
Additional reply just so you see it: this is the specific CB09 that I use(d) and it fit well into the holder.*
https://www.amazon.com/gp/product/B07D838BHJ
*disclaimer: while it does work well, I'm primarily using a Roland style blade/holder now with 3d printed adapter parts, as the blades are cheaper.
I can't speak from actual use yet, but here is what I've gathered.
This product was referenced above as high quality. I've also seen some on sites like etsy that seem to be reliable for fitting in the 4, in that the seller is specifically declaring that it fits.
https://www.therhinestoneworld.com/trw-cameo-graphtec-blade-holder
I bought this - it's been referenced in some posts as fitting the 4 plus reviews on Amazon indicate that it fits too.
https://www.amazon.com/dp/B07D838BHJ/ref=cm_sw_r_cp_api_glt_fabc_EWW4SM6RFE7W5GTB7AAK?th=1
What is your personality, plus how handy are you and what is your cheapskate factor?
No handiness and/or have no budget concerns ever - go with a variety of the Silhouette blades. $10 each, I think.
Mild ability to troubleshoot and desire to save: CB09, about $1 each. I personally have this specific one: https://www.amazon.com/gp/product/B07D838BHJ
Risk seeker: uses cheap Roland style blades, holder is a bigger upfront cost. I haven't jumped on it due to the lack of reviews and lack of need on my end. https://www.amazon.com/gp/product/B09PV7H11K
Tinkerer and possibly ultimate cheapskate: Roland holder with 3d printed holder (requires modifying the roland holder too). About $.30-40 a blade. https://www.amazon.com/gp/product/B07P8DMC2J and https://www.printables.com/model/44721-silhouette-cameo-4-adapter-for-roland-blade-holder