Congrats on getting married.

You are screwed. Availability on UA does not mean availability using LM.

If you provide a date range and dept-dest info others here can have a look as Lifemiles has some quirks when searching and there may be options that don't readily show up.

It won't help you now but 500k Amex points used for travel on Amex are worth $5K and if used with the right partner up to $10k - so best seek advice before transfering points.