What is the adjectival form for the word "integrity?"

Integrous

http://en.wiktionary.org/wiki/integrous

http://www.allwords.com/word-integrous.html

It doesn't pass a spell-checker, but there are over 500,000 hits for it on Google, most of which are using it precisely as you defined.

Virtuous: Having or showing virtue, especially moral excellence: led a virtuous life.

Note that integrity is the quality of being honest and having strong moral principles.

Be virtuous!

integrious Variations of usage found in literature include integrous and integritous, also with similar meaning.

Wiktionary:

integrious (comparative more integrious, superlative most integrious)
(rare) Marked by integrity.
Howard is an integrious man because his values are congruent with and evident in his words, actions, personality and life.

Most importantly, Wiktionary cites the reference of
The Oxford English Dictionary 2nd Edition Volume VII.

Considering the marking "rare" along with the OED citation, it appears that it is (or was) an authentic word.

Found something on the Why We Need the word Integrious movement!

I don't know of an adjective form of integrity, so I can't solve your issue directly. However, depending on if your use case allows it, you might consider the phrase Have integrity. Obviously if you're trying to offer a set of parallel Be X statements, this won't work, but if you're looking for a concise two-word imperative sentence, I think it carries the meaning you're looking for.