Is there a way to make a tier 4 ridgeball without using mutation liquid or buying a seed?

No

No didnt know u were still with us Borg nice to see a post from u lol

yes, but you need two of it like

Viola Ridgeball and Aureus Ridgeball = (replace flower here) Ridgeball

and in other ways, an absolute NO

There are two 'parts' to every species. Ridgeball is a Tier 4 foliage, and the two flowers named above are not Tier 4 flowers.

The only way to obtain either Tier 4 foliage or Tier 4 flowers is by using mutation liquid, breeding Tier 4 species that you already have, or purchasing exctinct seeds from the Supply Shop. Keep in mind, however, that the exctint seeds aren't always Tier 4. If you want to make sure that you are purchasing seeds that will produce either Tier 4 foliage, Tier 4 flowers, or both, you can refer to sfrose's seed catalog in the Plant Tycoon Guides.