we are attending a conference at a nearby hotel, do you have a shuttle or service?

Uber

do you have an airport shuttle?

There is normally no shuttle service serving Hilton Gaslamp, not even to the airport.

They always have one going when I've been in town! During Comic Con they were running about every 15-30 mins! 😊

It's a perfect location for the convention walking distance

There is not. But there is a taxi stop at the front.