I am willing to wager that sodium carbonate is available in every simple supermarket in the entire developed world, probably the undeveloped world too.
Look in your laundry aisle, in fact, look in your laundry you may well already have some.
Sodium carbonate is also called Washing Soda, you can also use Sodium Percarbonate, also known as Sodium Peroxyhydrate, which is the primary ingredient in "whitening" laundry powders.
I currently use "Sard Wonder OxyPlus".
With that said, your problem looks to be adhesion more than developer strength.
I always sand the PCB, if I don't, I get adhesion issues, I use a fine grade sandpaper, 400 or higher.
Also, read my tips:
http://sparks.gogo.co.nz/dry-film-tips.pdfAnd bigclive has done a number of videos also now.
I use a clothes iron.