You can search nearby medical equipment stores. The 5-liter oxygen generator is medical grade, and only medical equipment stores sell it in general physical stores. But now that e-commerce is so developed, you can choose it online, which is definitely cheap. For example, brands such as Youerkang, Yingweikang and Yuyue are all sold online.
I hope it helps you. Everything goes well. Please adopt it in time. Thank you.