Hi mate,
you can replace the BC184C with the MPSA18 which is a great transistor and readily available.
That's my advice use the MPSA18, just be aware that pinout is the oposite of the BC184, so the position in the board of the MPSA18 will be reversed compared to the BC184.
Only source that I know at the present for BC184C transistors, was a link posted by Ian (ruffrecords) some days ago:
The BC184C from Silicon-Ark have arrived. The first one tested had hFE = 515 @ Ic = 5mA, 2nd 529, 3rd 530, 4th 539 and 5th 547.
That's 10% of the number I bought so I am pretty confident they will all be over 500 ( I had to buy 55 of them the get to the minimum order value). Anyone who wants a few PM me and I will pop them in the post.