It’s easy to create your own spray cans. =)
Spray paint can be expensive and you might not be able to find the exact color you are looking for.
You can use any type of paint available acrylic, plastic, water based, food coloring, ink, permanent ink, etc.
(...with the only precaution that it won’t dissolve the plastic bottle itself )

Step 1: Materials + Tools

Materials
2-3 Bicycle inner tubes (used or old you only need the valve)
Coca Cola bottle (it’s made to withstand a lot of inner pressure)
Spray paint can ( EMPTY)
Plastic air tube (found at pet stores for aquariums)
simple plastic pen

Tools
hacksaw
awl
pliers
pliers cutter
bike pump
lighter

Step 2: COMPLETELY Empty Spray Paint Can Before Cutting It!

Very important!! COMPLETELY empty spray paint can before cutting it!
It should be empty of ANY air or paint residue.
…then pierce the can with the awl in an open & safe area, pressure might still exist in the can. You need to COMPLETELY remove the air before cutting the can this is important because the can might explode if any pressure still exists in it when you saw the top off.

Step 3: Remove As Mush Metal Around the Valve As Possible

With the pliers cutter and pliers remove as much metal around the valve as possible and remove any pointy edges.
You will end up with something looking like this.

Step 4: Cut the Valves Off the Bicycle Inner Tubes

With scissors or exacto knife cut the valves off the bicycle inner tubes.

Step 5: Pierce the Coca Cola Bottle

Heat the awl with the lighter and pierce the Coca cola bottle.
The hole must be as big as the bicycle valve to fit tightly.

Step 6: Create 3-4 O-rings From the Bicycle Spare Tube.

Create 3 O-rings from the bicycle spare tube.
place one on the valve that will go on the bottle.

Step 7: Insert the Valve on the Bottle

Insert the valve on the bottle.
With the pliers tighten the small nut from the outside of the bottle so the O-rings adhere to the bootle from the inside.

The bottle part is ready. =)

Step 8: Pierce the Coca Cola Bottle Cap

Heat the awl with the lighter and pierce the Coca cola bottle cap.
The hole must be as big as the bicycle valve.

Step 9: Create the Cap Valve

Cut the “valve part” from the valve.

Insert 2 O-rings one from the upper side & one from the inner side and secure tightly with 2 nuts.

Fit a piece of air tube on the inner side long enough to reach the bottom of the bottle.
(liquid will have to go through this tube to escape from the bottle)

Place another piece or air tube on the outer side of the bottle cap (as long as you want) and secure tightly with hot glue or zip ties this connection must be super secure. (you don’t want paint squirting everywhere!)

Step 10: Create the Can Valve Part

Stretch the air tube as to securely fit the plastic part of the can valve.

Take a piece of the plastic pen and stretch the end in a V shape to be able to fit tightly around the valve and the air tube.

Then gently hit it to insert the plastic pen part around the valve securely you can use a zip tie to keep it secure.
(you don’t want paint squirting everywhere!)

Step 11: You Are Ready =)

You are ready =)
Test the finished product with some water. Slowly increase the pressure inside and check for any leaks or moving parts…
If all is secure your spray painter is ready. A good indicator of how much pressure exists is when the label is stretched around the bottle.
Only fill half of the bottle with paint and leave the rest of the bottle for the compressed air to build up.
You are ready to use your spray painter!

*Tip for graffiti writers..
If you make the air tube on the upper part of the cap long enough, you can even make an undercover sleeve spray thingy ;)
just place the bottle part in your backpack and pass the air tube through your sleeve.

Have fun! =D