I can write the Turkish I know quite quickly but often find when trying to actually say it out loud I end up looking like a puffing goldfish!
Engaging brain to mouth is much harder but practicing does help and most Turks won't mind at all 
I'm exactly the same Nichola, the Turkish I know I can write very quickly and in the correct order. I'm quite comfortable speaking Turkish at the market and shops, possibly because they don't really know me. Like you sometimes when I try to speak my mind goes blank and then afterwards I know exactly what I should have said.
What helps me most is to be in the company of a Turk who speaks no English, then I have no option other tan to try. I have a couple of Turkish friends with very good English but some days they will only speak Turkish to me and make me answer in Turkish.
Wish I had made a concentrated effort to learn Turkish seven years ago when we first came and I was younger. From the beginning I had Get By in Turkish which consisted of a book and 4 discs that coupled with some other books gave me a basis and quite an extensive vocabulary. It was only a year ago that I started structured training which has helped immensely and I thoroughly enjoy. The next book I need to buy is 201 Turkish Verbs from Amazon.