I am not sure what you mean by keeping seeds “fresh”, but I presume you mean something like keeping them viable. It is to my understanding that seeds from most plants should remain viable for at least a year (obviously this varies from plant to plant) as long as they are kept in proper conditions.
Albuca Viscosa is a very cool plant! I do not have any seeds of it, nor will I really have many of the rarer plant seeds but a quick google search shows they should be quite easily accessible locally.
Would be useful to get a list of plants that you are looking for
It seems LA has a similar climate to the Western Cape, so cape succulents would probably fit your garden nicely. I could give a few suggestions on this.
Which seeds are you willing to trade from your side?
One thing to note is that shipping is quite expensive from South Africa to most other places in the world, so I will have to check the prices.