Drive to caddy:

www.parts-people.com/index.php

Others are listed there  as well - the screw that holds the caddy to the chassis is usually different than the ones that hold the drive in the caddy.

The 1505 caddy basically is a cover that goes over the front of the drive.

You need 2 M3 x 3mm screws

3mm x 3mm (M3x3mm) HDD screw - here

Dell™ Inspiron™ 6400/E1505 Service Manual - Documentation

Manuals - Documentation

Hard Drive

Dell™ Inspiron™ 6400/E1505 Service Manual

Removing the Hard Drive

CAUTION: If you remove the hard drive from the computer when the drive is hot, do not touch the metal housing of the hard drive.

CAUTION: Before you begin the following procedure, follow the safety instructions in the Product Information Guide.

NOTICE: To help prevent damage to the system board, remove the main battery (<ADMIN NOTE: Broken link has been removed from this post by Dell>) before working inside the computer.

NOTICE: To prevent data loss, turn off your computer before removing the hard drive. Do not remove the hard drive while the computer is on, in standby mode, or in hibernate mode.

NOTICE: Hard drives are extremely fragile; even a slight bump can damage the drive.

NOTE: Dell does not guarantee compatibility or provide support for hard drives from sources other than Dell.

1. Follow the instructions in <ADMIN NOTE: Broken link has been removed from this post by Dell>.
   
   
2. Turn the computer upside-down and remove the two M3 x 3-mm screws.
   
   

NOTICE: When the hard drive is not in the computer, store it in protective antistatic packaging. See "Protecting Against Electrostatic Discharge" in your Product Information Guide.

1. Slide the hard drive out of the computer.

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I bought mine from eBay. Here is an example.

ejn63. In total there are 4 screws. 2 attach the caddy to the harddrive. (M3×3mm)

Then two attach the top of the harddrive to the base plastic of the system. (M3×3 mm). So the 4 screws are the same in this system and the picture in the service manual is somewhat misleading.