555 astable operation not getting stable frequency
If you're building an oscillator for communication purposes, C-charge based oscillators won't do – aside from a very few speciality devices, capacitors are rated for 5%, 10% or even 20% tolerance. So I'd say your circuit operates well within the physical boundaries of what your components offer.

I'd strongly recommend just getting something that has a trimmed internal oscillator – that something might actually be an 38 kHz oscillator, or, even simpler, a microcontroller generating 38 kHz with e.g. a PWM unit. This option sounds twice as reasonable considering that when communicating over IR, you most probably already have some digital logic!