A disposable blade ryoba (double sided saw) can be had at almost any tool store, like Woodcraft, Lee Valley if you're Canadian or close to it, or even Home Depot. Amazon also carries good brands, and Woodcraft along with Japan Woodworker (a tool importer bought out by Woodcraft) have online stores.

Gyokucho is my favorite brand. More important than the brand is what you will be cutting; Japanese saws have progressive tpi: smaller and more numerous teeth at the base of the saw, where you start your cut, generally getting large near the end, especially on rip profiles. Even with that, they still have different sizes for different uses. 180mm, 240mm, 300mm are the most common sizes for ryobas. 150mm for thin stock and precise work, 300mm for breaking down rough stock or thick stock joinery like in timber framing, 240 as a general, jack-of-all-trades.

Secondly, as Americans have fallen in love with Japanese blades, Japanese manufacturers took notice and now produce saws with tooth profiles suited for American hardwoods- although even American softwoods are still sometimes harder and more prone to breaking teeth of Japanese softwood saws than Japanese softwoods.

If you do cut American hardwoods often, here is a general purpose ryoba: https://www.amazon.com/Gyokucho-Double-Ryoba-RazorSaw-Hardwoods/dp/B001Y4ZUJW/ref=sr_1_2?keywords=hardwood+ryoba&qid=1564430848&s=gateway&sr=8-2

It's a disposable blade, once you dull it you can replace it. Even so, I usually use a joint powertool-handtool process, and have that exact hardwood saw for three years now and it's still just as sharp.