H&M standard maternity jeans are plenty long enough for me at 6ft tall. ASOS also worth a look: they have maternity jeans in longer lengths. My maternity jeans fit me better than my non-maternity ones, I love them!
Gap is good, or an online brand called mummy long legz. Seraphine also good as dresses are generally a bit longer. I find next jeans are not long enough (their long leg is 33") and didn't find much in the topshop maternity section- but it depends on if you want under or over bump jeans. I prefer the over bump ones. Good luck!
I'm 5 foot 11 and find H&M maternity jeans great. Sometimes mamas and papas maternity trousers are long and these have been great for work. Personally I find jojo maman bebe far too short, their trousers come up well above the ankle on me!!
I bought from gap, v long and jojo do different leg lengths, i lived in a pair of jojo over the bump from week 32 as they were so comfy, although do cone up big, so worth trying on if you can get to a shop?