Here's a pattern I've used many timess successfully in the past:

• Force all parsers to use a specified namespace (e.g., EP::Parser::Soemthing)
• In your main class (e.g., EP::Parser) have a routine that runs at 'use' or 'require' time that use something like Module::Find to find all modules in the specified namespace.
• Iterate through the modules and 'require' each of them

Since this runs whenever the module is loaded it will complain at startup if one of the implementations is incorrect.

For another layer of abstraction you can combine the above with use of Class::Factory as the parent class and associating each of the implementations with a simple name rather than a class name.