Haven't really parsed volume 3 much.... but:
Here's what gomanga.com (Seven Seas) has so far for translated manga release ... what they don't have is any linkage to a vendor yet. It'll be interesting to see how this gets handled.
Nymphet:
Volume One
Street Date: April 2007
Price: $10.99
Format: Manga
Trim: 5" x 7.5"
Page Count: 192
Age Rating: Older Teen
ISBN: 978-1-933164-47-2