Question: Is there an instrument that can produce a sub bass sine wave like tone, that also has a lot of volume? Something that would sound a bit like an 808 bass.

I've listened to some contrabass type flutes but it sounds very breathy and there are too many overtone sounds.

I know that an ocarina produces a tone that comes close to a sine wave. Here is an example of a giant bass ocarina which comes close, but sounds a bit soft and underwhelming.

Answer: 
There really is no such thing as a sub bass sine like tone with a lot of volume. There are some organs with 32" subbass flutes (which produce a comparatively sine-like tone). They are monstrous in size and move a lot of air, but due to the limits of human hearing, the audible volume is not all that large. You feel their effect a lot more than you hear it.

It's one reason that motor bass/subbass speakers have been prohibited for concert use: they don't have a lower frequency limit like cone speakers, and people exposing themselves to excessive subbass noise have actually died of spleen rupture.

So the closer you get to your "sine wave" ideal, the more certain it is that you'll find the results "a bit soft and underwhelming". Actually "strong" bass instruments almost invariably have significant amounts of overtones. And since it is the overtone interaction that makes for the bass functioning as a harmonic foundation, really low sine tones tend to be harmonically arbitrary: if you are off by a tone or so, it doesn't really register all that much in terms of being disharmonious.
What do you mean by sub bass? Are you referring to a sub harmonic of the instrument?

I will assume you are asking whether an instrument can produce a pure sine wave.

It would be very unlikely to get a pure sine wave from a musical instrument. Even a function generator will produce transient harmonics due to being "switched on". Without getting into the details of the math and physics, the specific harmonic spectrum of the instrument depends on (1) what overtones are supported by the physics of the instrument construction and (2) how the instrument is attacked, or how sound is excited in the instrument. Additionally, the harmonic spectrum can depend on time. It may be bright at first then decay, leaving mostly the fundamental (which would be as close as possible to a pure sine wave). The guitar and other plucked instruments have this property.

If you pluck a guitar string close to the center you excite more fundamental but you still do not have a pure sine wave. I would say that it is very unlikely that any instrument and player could produce this. At the very least there would be harmonics for a short time due to starting the sound.

As a side note, the human ear is non-linear and creates aural harmonics. So, even if you use a function generator as an input the signal to the brain will be "corrupted" with harmonics.

If you are referring to an instrument producing a true sub-harmonic. I is possible but most so called examples of a sub-harmonic are false. They are the result of changing boundary conditions in the attack and people completely misunderstand the physics of what's going on.