I have been moving my development level to tier 3 with a swift pace by getting frequent 1000 xp from individual doff mission. My diplomacy level has been slow with doff missions ranging from 50 to 200 xp. Are there doff missions that have 1000 xp? Thanks.

Most of the Diplomatic missions only offer small change like that, the few that are over a thousand DXP are rare or unique and part of assignment chains.

The only way to get Diplomacy-XP quick, is to produce constantly critical successes on Entertain Foreign Dignitaries. If you've got a whole purple-Doff-Set for that assignment, you also get a quality-reward-bonus of 100%.

All the other Doff-Assignments reward only small amounts of Diplomacy-XP and can't be boosted to more then 25% critical success chance.

There's a few other options too. Head out to cardassian space and do some of the chains, especially the "Consular Authority".
http://www.stowiki.or/Assignment:_De...man_Government
http://www.stowiki.org/Assignment:_I...ate_on_Karemma

Crits can knock these two up very high and you can do 4 the chain 4 times.

And while not in the same league, http://www.stowiki.org/Assignment:_H...ious_Symposium is also pretty good.

But I agree that foreign dignitaries is pretty much the best.

I don't know of one mission that gives a huge amount of XP, but there are always a bunch of little ones.
Check your available missions for diplomatic missions. I can't remember what it's called but there's a mission that pops up after tier 1 or 2. They're not DOFF missions, but they are quick, easy, and in the same star clusters as the colonization chains.

Your first link is broken, let me fix that:
http://www.stowiki.org/Assignment:_D...man_Government

Well, you can do these assignments only 1 time each (if you don't fail them), for a repeated grind on Diplomacy-XP that doesn't matter much.

First Contact Missions and Diplomatic Investigations... Those are also just "little points".

I have found tons of diplomacy assignments near DS9 and up near Defera. I was having major issues with diplomacy so I ended up getting like 15 diplomats and did all the DS9 area diplomacy missions for a couple of weeks and finally got there pretty fast. Also, if you get bored, you can do the diplomacy missions under the hail starfleet tab. They are fast, taking only a couple of minutes, but they only give about 50 diplomacy. It's better than nothing though considering they amount you get. If you happen to have any CXP boosts, those help as well. You can buy CXP boosts from the c store or from the exchange.

Thanks all for the tips!

They give 100 Diplomacy XP each.

Get a group of three people, each of you take Diplomatic Investigation (Delta Volanis), Explore Strange New Worlds, and Explore the Delta Volanis Cluster.

In under five minutes, you can get 1440 Dilithium, some skill points and XP, and 300 Diplomacy XP, just by doing each persons Diplomatic Investigation mission in turn.