Safariland Model 5187 holster- Glock 20/21 with light rail

The 5187 incorporates Safariland's new adjustable belt loop, allows adjustment for straight hang, forward cant or crossdraw. A compact, lightweight concealment holster available for handguns with accessory rail mounted lights. IDPA approved.Accepts 1- 1/2" wide belts.Holster is lined. This model comes with an accessory spacer so that the user can adjust the space between the holster and body. This holster accepts Glock 20/21 pistols equipped with the Streamlight or Surefire rail-mounted flashlight.

Here are some sites that sell the holster:
(prices are at the time of article)

Dillon Precision - 39.99
Midway USA - 36.00
CopQuest - 39.20