where can i buy a head gasket sealant / head gasket cooling seal? something like blue devil or similar.

No idea. However (if it works) it's only a temporary solution (i.e. if you want to sell your car). It's like the old remedy to put sawdust in your gearbox to quieten it.

its an old car but drivable, have a little of white smoke out the pipe nothing major, nothing noticeable, only if you pay really closed attention, not worth the money to replaced the head gasket, i try autobac they don't have it, any other store to recommend.

Do you mean radiator sealant ? as I don't know of anything that will seal a head gasket leak without taking off the head ? And if you are taking off the head you might as well put a new gasket on. If it is an old car it will cost very little. White smoke also isn't really a sign of a blown head gasket either. Overheating and water in the oil are. Take off the oil filler cap on the top of the engine. if it has a white creamy goo around it the heads gone. also take out the dipstick and check the colour of the oil. If the head has gone it will be a white colour where the oil has emulsified with the water.

If all you are getting is some white smoke then I wouldn't worry too much if it is an old car

it is a radiator sealant type but it works particularly for small minor head gasket leak, oil cap is clean no mildew, dipstick is also clean.

it is a radiator sealant type but it works particularly for small minor head gasket leak, oil cap is clean no mildew, dipstick is also clean.

Then don't worry (Yet). . Nothing seals a blown head gasket.

it is a radiator sealant type but it works particularly for small minor head gasket leak, oil cap is clean no mildew, dipstick is also clean.

Then don't worry (Yet). . Nothing seals a blown head gasket.

...or a cracked head.

it is a radiator sealant type but it works particularly for small minor head gasket leak, oil cap is clean no mildew, dipstick is also clean.

Then don't worry (Yet). . Nothing seals a blown head gasket.

...or a cracked head.

Yep, a minor crack in a head might only shift water at a certain temp, the expansion and contraction thingy.

it is a radiator sealant type but it works particularly for small minor head gasket leak, oil cap is clean no mildew, dipstick is also clean.

Then don't worry (Yet). . Nothing seals a blown head gasket.

...or a cracked head.

Yep, a minor crack in a head might only shift water at a certain temp, the expansion and contraction thingy.

Spot on hence the puff of white smoke.

crack an egg in there... that should sort it out.