Hi Cherry,
I have seen Pearl Bordered Fritillaries, as well as most of the other British species - but I've travelled around most of the country.
If you look at the data that 'Butterfly Conservation' have entered on the NBN Gateway, there are none in our area (apparently none recorded in Herts since 1960). Note that the NBN Gateway does show records in Herts, but if you remove the data from Natural Englands Invertebrate Site Register, which is often unchecked and can be inaccurate, these all 'dissapear'.
There are sites in Surrey and Sussex (+ elsewhere in the country) and I can probably find you sites to try for these, or other species, if you are willing to travel, or if you are travelling for other reasons.
Roy.