Could anyone mention the names of Super C

Jayco is one

This one seems interesting but expensive. https://www.ddrv.com/inventory/new-2018-dynamax-isata-5-30fw-mh-xxxxxxxxxxx670016

Google search on "Super C RV" and had about a bazillion hits.

Try this site, I just picked a random one, I have no association. Forest River and Thor are listed: Click here.

30 ft with a small diesel might be a tad difficult to locate. Im not 100% sure but as far as I know, it might a difficult task. I can't think of any.

Normally small diesels are under 30 ft . Also built on lighter chassis like Ford or M. Benz with 16" wheels and light duty truck parts.
When you get into 30 ft diesel class c's, its 35 ft plus sizes w/350-600 HP engines running 19.5" / 22.5" wheels on a Freightliner chassis.
You are getting into big bucks territory to maintain them. Parts are off the chart compared to lighter duty trucks. I hope you can do the work yourself and have a barn to work in, otherwise you'll need experienced truck mechanics and not rv dealership mechanics. These are specialty shops with specialty hourly rates.

Here is a link to some.
Also look at Nexus.
When you say small diesel engine. How small.