Some exhibit/booth areas are staffed by knowledgeable people who are happy to answer questions, chat and/or listen to ideas for using or improving their products.
> no base point to start a conversation
How about the topic of the talk?
If you ask a question during Q&A, others may be interested and approach you to follow up.
> like a dating site except with no bio
Conference speakers typically have public bios and photos, which helps with hallway recognition. Those who are open to talking can often be found in a small group, which can be joined via topical comment/question.
But usually such very big shows happen somewhere in the USA/UK/west Europe etc. And pricey. What I've seen in my country were usually a conferences structured like a series of talks with breaks. If conference is big then 2 or 3 treks in parallel in different room. In this case there is only one point of interest - the presenter, and maybe one or two previous or next presenters. It's not a problem to recognize presenter, a problem is talk to him/her longer than a single carefully prepared question and answer, because there are like 20 other people around all trying to talk to him/her.
If enough people want to talk to a presenter, the conversation usually moves outside the presentation room to allow more time. It is worth listening carefully to the questions of others in the queue, since you may meet someone with a question close to your interests.
Limited time is a challenge, but it's also good practice for developing a short pitch about a question or topic. If successful, the goal should be to exchange contact info with the presenter, for a longer discussion at the same conference.