All items available through http://www.mcmaster.com

Simply search for the part #s listed. Total cost of supplies listed is around $90 plus shipping. 
You will have enough excess of most materials to make atleast 2 or 3 more guns.


Part#	 - Description						 = Price & Amount
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2522A717 - General Purpose High-Speed Steel Hand Tap Plug, 6-32, H3 Pitch Diameter, 3 Flute = $3.48


8574K28 - Polycarbonate Sheet 1/4" Thick, 12" X 12", Clear = $12.79 Each

8574K26 - Polycarbonate Sheet 1/8" Thick, 12" X 12", Clear = $6.96 Each

8702K61 - Polyethylene (UHMW) Rectangular Bar 1/4" Thick, 1/2" Wide = $3.20 for 5 feet

8541K18 - Black Nylon 6/6 Rod 1/2" Diameter = $1.02 per foot (5 feet) = $5.10 Each

8538K23 - Nylon 6/6 Rod 1" Diameter = $3.17 per Ft.

8585K43 - Polycarbonate Round Tube 1-1/2" OD, 1-3/8" ID, Clear = $3.48 for one Foot

8865K122 - Tear-Resistant Polyethylene Foam Thick Sheet 3/4" Thick, 12" X 12", Plain Back, Gray = $6.91 Each  (also available in White or Pink)

$42.14

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4880K314 - Std-Wall (Schedule 40) White PVC Pipe Fitting 1" X 1/2" Sz, Pipe End Male X Socket Fem, Hex Bushing = $0.74 Each

5308T347 - Hard Buna-N O-Ring AS568A Dash Number 316 - $3.68 per Pack of 50

9637K26 - Continuous-Length Compression Spring Spring-Tempered Steel, 11" L, .844" OD, .08" Wire - $10.12 per Pack of 5

9657K39 - Steel Compression Spring Music Wire, 1" L, 1/4" OD, .020" Wire Diameter = $6.04 per Pack of 12

$20.58

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90309A154 - Zinc-Plated Brass Unthreaded Round Spacer 3/8" OD, 1/4" Length, #6 Screw Size = $0.57 Each (2) = $1.14

91780A125 - Aluminum Female Threaded Hex Standoff 1/4" Hex, 3/8" Length, 6-32 Screw Size = $0.34 Each (2) = $0.68

91780A131 - Aluminum Female Threaded Hex Standoff 1/4" Hex, 3/4" Length, 6-32 Screw Size = $0.44 Each (3) = $1.32

91780A337 - Aluminum Female Threaded Hex Standoff 1/4" Hex, 1-1/2" Length, 6-32 Screw Size = $0.78 Each (2) = $1.56

$4.70

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90402A144 - Zinc-Plated Steel Pan Head Phil Machine Screw External Washer, 6-32 Thread, 1/4" Length = $5.36 per 100

90402A146 - Zinc-Plated Steel Pan Head Phil Machine Screw External Washer, 6-32 Thread, 3/8" Length = $5.31 per 100

90631A007 - Grade 2 Hex Nylon-Insert Locknut Zinc-Plated Steel, 6-32 Screw Sz, 5/16" W, 11/64" H = $1.85 per Pack of 100

90295A075 - Nylon 6/6 Flat Washer #6 Screw Size, .140" ID, .313" OD, .057"-.067" Thk = $2.68 per Pack of 100

$15.20

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Items you can find at any hardware store in smaller quantities.
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98637A155 - MIL Spec Alloy Steel Cup Point Set Screw Cadmium Plated, 6-32 Thrd, 3/8" Length, MS51963-24 = $2.29 (you only need one)

90272A159 - Zinc-Pltd Stl Pan Head Phillips Machine Screw 6-32 Thread, 2" Length = $5.71 per Pack of 100 (you only need one and you can also use a threaded rod)

90272A155 - Zinc-Pltd Stl Pan Head Phillips Machine Screw 6-32 Thread, 1-1/4" Length = $2.96 per pack of 100 (you only need one)

90272A153 - Zinc-Pltd Stl Pan Head Phillips Machine Screw 6-32 Thread, 1" Length = $2.62 per pack of 100 (you only need two)