How to install pip3 in Ubuntu 18.04 on a bootable flash drive?

Question

ubuntu

There is Ubuntu 18.04, loaded from a flash drive in the "Try without installation" mode. When I try to install pip3: the
sudo apt install python3-pip
console outputs:
E: Unable to locate package python3-pip
At the same time, git, for example, is perfectly installed. What's wrong? Does the install image use other/reduced repositories?
Why is it necessary?
There is a laptop with Windows on which you can not put Ubuntu. I came up with the idea of ​​​​running liveusb, installing the necessary software with scripts and coding in cozy Ubuntu. But so far it hasn't worked out.

Answer 1

As a way out, you can download the .deb package from here and then install via:
sudo dpkg -i python3-pip_9.0.1-2_all.deb