Is any way to improve the chances of a solar eclipse happening (apart from killing the mechanical bosses). Basically I want to get broken hero swords to be able to forge the terra blade...
Based on this answer, you can summon a solar eclipse with the Solar tablet at any point in daytime since v1.3 (on PC version).
A solar tablet can be crafted from 8 solar fragments on a hardmode anvil.
Solar fragments can be looted from the lizahrd temple mobs & chests, and you can even find a full tablet in a chest.