The following prayer is my own composition:
We have been taught by the legend of St George
to fight against dragons and to rescue the helpless.
Deliver us by the truth of the gospel
from that great dragon who leads the whole world astray.
Free us from our slavery to sin and death.
And grant that your light may dawn again on this nation of England.
Through Jesus Christ our Lord,
Another prayer that might be suitable for assemblies:
Heavenly Father, give us the bravery of St George to stand up for what we believe. Give us the strength to overcome the dragons in our lives and in the world. And where we see people in distress, give us the compassion to help them. Amen
The following prayer is from "THE ORDER OF SERVICE AT MATTINS ON THE OCCASION OF THE 80TH BIRTHDAY OF HER MAJESTY THE QUEEN AT ST GEORGE'S CHAPEL, 23 APRIL 2006". I do not know anything other than that about the source:
The collect for St George's Day
O God of hosts, who didst so kindle the flame of love in the heart of thy servant George that he bore witness to the risen Lord by his life and by his death: grant us the same faith and power of love that we, who rejoice in his triumphs, may come to share with him the fullness of the resurrection; through Jesus Christ our Lord. Amen.
There is also this, given as the Collect for St George's Day, in Franz Hildebrandt: Mr. Valiant-for-Truth:
O Lord God of hosts who didst give grace to Thy servant George to lay aside the fear of man and to confess Thee even unto death, grant, we pray Thee, that we and all our countrymen who bear office in the world, may think lightly of earthly place and honour and rather seek to please [Jesus] the Captain of our salvation who hath chosen us to be His soldiers, to whom with Thee and the Holy Ghost be thanks and praise from all the armies of thy saints, now and for evermore. Amen.