This post in a github discussion explains why components like combo-chart (useful but a bit more complex) aren't included in the ngx-charts library. Instead, those use cases are featured in the demo section, where you can view the source code and the final look and feel.
As far as I can tell, the best way to integrate the combo-chart is to create a combo-chart.component in your own project and copy the source code into it. You will need to include the ngx-charts library and change any imports that rely on the local structure of the demo to point to that library instead.
For example, in combo-chart.component.ts
import { NgxChartsModule, <other imports> } from '../../src';
would become
import { NgxChartsModule, <other imports> } from '@swimlane/ngx-charts';