I am trying to reproduce this command circuit of a JFET semiconductor: and there are many components I am struggling to reproduce in LTspice. For instance, for the dc-dc converter, does LTspice provide a simple model or do I have to remake it from scratch? Also, this figure is a screen shot of the datasheet of the component of interest. Is an IXDD component an "AND component"? and What about the Opto part? This has been bothering me for quite a while now. I woud be very appreciative for pieces of advice and your help.
Making a model is not easy work. Your interest should be the behaviour of the model, not the exact, nitty-gritty details of its internals. That's not to say that you can't go that way, there are people who made transistor-level 741s, and more, but those models will also be very slow in terms of simulation time.
Therefore, as AJN mentions, the converter can be replaced by a voltage source, referenced to the local ground. IXDD509 seems to be an IXYS component. And the opto-coupler, is an opto-coupler. Unless there are specifics about it, a diode and a current sensor should do (or even some voltge/current source, for even more simplicity).