Find one from another year, make or model. It not rocket surgery. Something around the same shape, size and volume.

What size is your cracked bottle?

 

The problems is the scarcity of the parts. It is about 500ml.

 

There's one on eBay - 91 1991 Polaris Trail Boss 350L 350 Four Wheeler Engine Oil Fuel Coolant Bottle | eBay

 

That is the oil reservoir, not the coolant reservoir.

My oil system doesn't work, so I mix the oil and gas.

 

id get one from a new model value line atv say like my 13 sportsman 800 has 2 bolts that mount to a frame rail and a line from rad to reservoir likely easy enough to make it fit and work I can get a pic if needed ,

 

id get one from a new model value line atv say like my 13 sportsman 800 has 2 bolts that mount to a frame rail and a line from rad to reservoir likely easy enough to make it fit and work I can get a pic if needed , 454 2003 Polaris Sportsman 500 4x4 Coolant Tank | eBay

 

1 liter mountain dew bottle will do it just fine

 

Give JB Weld a try. I like this guys test.

 

Love this guys tests

 

Plastic welding is pretty easy.If I can do it anyone can .they have plastic welding kits at harbor freight. I just use a solder iron .Most impressive one Iv done is the rear rack on the 850 .Broke a 4" chunk off where the bolt holds the rack to the frame It was definitely a high stress point , but it held till this day. V it out and fill it in with the same type of plastic