Yes, I'm having problems sharpening my chisels to 30°. The basic problem
seems to me to be that my sharpening stone is far far too fine. It's in
perfect condition, but is probably quite a lot older than me and is marked
"Bauxilite 479 Medium". Bauxilite is of course the abrasive material, I've
managed to figure that one out, but the number is meaningless and "Medium"
is a very subjective term. I have some brand new chisels to sharpen, already
ground to 25° but blunt, and some old ones which due to years of horrible
mistreatment really could do with regrinding to 25° before I grind them to
30°.

snip

Before I roam the local DIY and tools stores, any advice?

If the stone is too fine you need a coarser stone - seems obvious to
me.
For grinding I use either a belt sander with 60 grit, or an angle
grinder with a grinding wheel not a cutting wheel.
I then hone on a stone with bike oil thinned a bit with white spirit.
The stone is 30 years or more old bought from Woolworths for 5 bob or
something. I somtimes use a honing guide to get the angle perfect but
then do it by eye for re-touching. The most important thing with an
oil stone (after getting the grade right) is to wipe it clean
immediately after using it and to put the lid back on. Then It will
never clog up or need cleaning.

cheers

Jacob