We don't have good midrashim books here in our town.
Do we have the story of Purim with good midrashim in english on the net?
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Chabad.org has a online (all English) "Megillah With In-Depth, Side by Side Commentary" which you may find useful.
There is in Otzar Hachachma (first 40 pages are free, but the rest must be paid for).