According to the PI Interface for GE iFix User Guide, history recovery is not supported and hence the interface is not an option for you.
Because you mention the files to be of type *.iha, I understand you may be looking for a way to convert those files to PI Data Archive files. I wouldn't know we've ever offered something which does conversion file based and I doubt this will ever be considered a valid option. Not because we don't believe this could be useful but because the 'foreign' format must be considered intellectual property of the other vendor.
The next question is what protocols you have available to access historical data (OPC HDA, RDBMS etc.)?
If available protocols do not suggest any PI Interface or PI Connector, what programmatic options do you have to access the data? Those could be used for a direct or indirect (e.g. through comma separated files) data migration.