The fire in homa shouldn't be used from petroleum based products at any cost. So, that case is eliminated. Homa especially mentioned in tantras are used to bend the energies in the nature and do whatever is intended by homa over a long period of time. Fire is seen as a universally available source and at different places at appropriate conditions that fire is experientable(in modern terms generated). This more evident when the process of agni-shuddhi at the start of homa is analyzed. So, the place from which fire is generated/source should be as natural and fire should be new and immediate as possible is the idea so that suddhi can be done easily and assuredly with our own hands. There is no involvement of a third person out of the mentality and sanctity of the homa doer. But in the present situations it isn't possible for us to go to that extent often like if the homa is done once or twice a year its possible for doing in the prescribed way. Or if homa is a big one involving devatas with ugra kala its better done in the old format. But when, homa is like a daily one or is done very often, due to time constraints or lack of resources or lack of physical strength etc., it won't be possible. Then, do any of the following:
- Ask your elders or anyone with high experience in this topic in your area(because the products would then be locally available) as they too would be facing similar issues.
- If no one is there to guide you regarding this. The process I've seen from people doing is; heartfully, first do kshama prarthana, then light a good quality camphor/agarbatti with a deeparadhana kundi (in which the universal form of parabrahma is invoked) and then place it in the kundam and start with homa.
If by tantrika homa you mean tantra shastras involving sadhanas of dasmahavidyas, chandika, pratyanghira and any other godess with high ugra kala. I don't know how much apt point 2 will be as these homas directly involve shakti. So, just am not sure there.