I needed some fittings when I did my conversion the other week and AutoZone had an entire end cap, behind the counter, of fittings and straight line sections. I was pretty impressed at the amount of fittings they had. The small fittings that use a 3/8" wrench are very com, that's the size that goes in the flex lines and distribution blocks.
The only place you'll get actual pre-bent lines for these cars is where you got the ones you have now, plus a couple other vendors.
If you have a flare tool you try to re-flare the lines if you see they are out of round or screwed up. If they look good they should tighten up eventually.
Are you using flare wrenches
when you tighten the lines? I had one line that I thought I was going to twist off to get it to seal.