Is there any fully digital (i.e. searchable) edition of the סליחות? Is it publicly available online?
Another place to look is Hebrewbooks.org (search for סליחות). They've got several editions, some of which have been OCR'ed and are therefore searchable.
Selichot for various eidot can be found at http://daat.ac.il/daat/sidurim/shaar-2.htm
Try this link to one Selichos edition on Google Books. There is a search box on the left side with which you can find text in that particular edition. Not perfect, but fairly useful. There are probably other editions available there as well.