These are literal translations. 貴社ますますご盛栄のこととお喜び申し上げます。 I congratulate that your company is prospering more and more. 平素は格別のご高配を賜り、 厚くお礼申し上げます。 I express my deep gratitude for your special consideration to us everyday. These are the formal and routine（＾＾； greeting words on Japanese business letter.

Something like this, "Please accept our congratulations on the ever-growing prosperity of your company. We would like to express our thanks for your loyal patronage." In Japan we use various floral openings like these in business letters.